Fix converter unit tests on Oracle

Error while converting via CommandLineService

org.nuxeo.ecm.core.convert.api.ConversionException: Error while converting via CommandLineService
	at org.nuxeo.ecm.platform.convert.plugins.CommandLineBasedConverter.execOnBlob(CommandLineBasedConverter.java:166)
	at org.nuxeo.ecm.platform.convert.plugins.CommandLineBasedConverter.convert(CommandLineBasedConverter.java:93)
	at org.nuxeo.ecm.core.convert.service.ConversionServiceImpl.convert(ConversionServiceImpl.java:205)
	at org.nuxeo.ecm.platform.convert.tests.TestPDFToImage.testConverter(TestPDFToImage.java:97)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.nuxeo.runtime.test.runner.FeaturesRunner$15.evaluate(FeaturesRunner.java:467)
	at org.nuxeo.runtime.test.runner.FeaturesRunner$BeforeMethodRunStatement.evaluate(FeaturesRunner.java:346)
	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
	at org.nuxeo.runtime.test.runner.FeaturesRunner$BeforeSetupStatement.evaluate(FeaturesRunner.java:362)
	at org.nuxeo.runtime.test.runner.FeaturesRunner$AfterMethodRunStatement.evaluate(FeaturesRunner.java:393)
	at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
	at org.nuxeo.runtime.test.runner.FeaturesRunner$AfterTeardownStatement.evaluate(FeaturesRunner.java:412)
	at org.nuxeo.runtime.test.runner.FeaturesRunner$RulesFactory$1.evaluate(FeaturesRunner.java:525)
	at org.junit.rules.RunRules.evaluate(RunRules.java:20)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
	at org.nuxeo.runtime.test.runner.FeaturesRunner$AfterClassStatement.evaluate(FeaturesRunner.java:285)
	at org.nuxeo.runtime.test.runner.FeaturesRunner$RulesFactory$1.evaluate(FeaturesRunner.java:525)
	at org.nuxeo.runtime.test.runner.FeaturesRunner$BeforeClassStatement.evaluate(FeaturesRunner.java:268)
	at org.junit.rules.RunRules.evaluate(RunRules.java:20)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
	at org.junit.runners.Suite.runChild(Suite.java:127)
	at org.junit.runners.Suite.runChild(Suite.java:26)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:160)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:138)
	at org.apache.maven.surefire.junitcore.JUnitCoreWrapper.createRequestAndRun(JUnitCoreWrapper.java:113)
	at org.apache.maven.surefire.junitcore.JUnitCoreWrapper.executeEager(JUnitCoreWrapper.java:85)
	at org.apache.maven.surefire.junitcore.JUnitCoreWrapper.execute(JUnitCoreWrapper.java:54)
	at org.apache.maven.surefire.junitcore.JUnitCoreProvider.invoke(JUnitCoreProvider.java:134)
	at org.apache.maven.surefire.booter.ForkedBooter.invokeProviderInSameClassLoader(ForkedBooter.java:200)
	at org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:153)
	at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:103)
Caused by: org.nuxeo.ecm.platform.commandline.executor.api.CommandException: Error code 1 return by command: convert -define registry:temporary-path=#{nuxeo.tmp.dir} -quiet #{sourceFilePath} #{targetFilePath}
Error: /undefinedfilename in --showpage--
  Operand stack:
     1   true
  Execution stack:
     %interp_exit   .runexec2   --nostringval--   --nostringval--   --nostringval--   2   %stopped_push   --nostringval--   --nostringval--   --nostringval--   false   1   %stopped_push   1916   1   3   %oparray_pop   1915   1   3   %oparray_pop   1899   1   3   %oparray_pop   --nostringval--   --nostringval--   2   1   1   --nostringval--   %for_pos_int_continue   --nostringval--   --nostringval--   1793   0   9   %oparray_pop   --nostringval--   --nostringval--
  Dictionary stack:
     --dict:1178/1684(ro)(G)--   --dict:1/20(G)--   --dict:82/200(L)--   --dict:82/200(L)--   --dict:113/127(ro)(G)--   --dict:292/300(ro)(G)--   --dict:28/32(L)--   --dict:6/8(L)--   --dict:21/40(L)--
  Current allocation mode is local
  GPL Ghostscript 9.10: Unrecoverable error, exit code 1
  convert.im6: Postscript delegate failed `/opt/jenkins/workspace/master/nuxeo-master-fullbuild-part1-multidb-linux/Slave/MULTIDB_LINUX/dbprofile/oracle12c/jdk/java-8-oracle/nuxeo-services/nuxeo-platform-convert/target/test-classes/test-docs/hello.pdf': No such file or directory @ error/pdf.c/ReadPDFImage/677.
  convert.im6: no images defined `/opt/jenkins/workspace/master/nuxeo-master-fullbuild-part1-multidb-linux/Slave/MULTIDB_LINUX/dbprofile/oracle12c/jdk/java-8-oracle/nuxeo-services/nuxeo-platform-convert/target/nxruntime-main-7004983083247025258.tmp/tmp/pdf2image_1471499101601/hello.png' @ error/convert.c/ConvertImageCommand/3044.
	at org.nuxeo.ecm.platform.commandline.executor.api.ExecResult.<init>(ExecResult.java:62)
	at org.nuxeo.ecm.platform.commandline.executor.service.executors.ShellExecutor.exec(ShellExecutor.java:83)
	at org.nuxeo.ecm.platform.commandline.executor.service.CommandLineExecutorComponent.execCommand(CommandLineExecutorComponent.java:173)
	at org.nuxeo.ecm.platform.convert.plugins.CommandLineBasedConverter.execOnBlob(CommandLineBasedConverter.java:157)
	... 50 more