Fix random test failure on picture tiling

java.lang.AssertionError: 
	at org.junit.Assert.fail(Assert.java:91)
	at org.junit.Assert.assertTrue(Assert.java:43)
	at org.junit.Assert.assertTrue(Assert.java:54)
	at org.nuxeo.ecm.platform.pictures.tiles.service.test.TestService.testGC2(TestService.java:357)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at org.junit.internal.runners.TestMethod.invoke(TestMethod.java:66)
	at org.jmock.integration.junit4.JMock$1.invoke(JMock.java:37)
	at org.junit.internal.runners.MethodRoadie.runTestMethod(MethodRoadie.java:105)
	at org.junit.internal.runners.MethodRoadie$2.run(MethodRoadie.java:86)
	at org.junit.internal.runners.MethodRoadie.runBeforesThenTestThenAfters(MethodRoadie.java:94)
	at org.junit.internal.runners.MethodRoadie.runTest(MethodRoadie.java:84)
	at org.junit.internal.runners.MethodRoadie.run(MethodRoadie.java:49)
	at org.junit.internal.runners.JUnit4ClassRunner.invokeTestMethod(JUnit4ClassRunner.java:98)
	at org.junit.internal.runners.JUnit4ClassRunner.runMethods(JUnit4ClassRunner.java:61)
	at org.junit.internal.runners.JUnit4ClassRunner$1.run(JUnit4ClassRunner.java:54)
	at org.junit.internal.runners.ClassRoadie.runUnprotected(ClassRoadie.java:34)
	at org.junit.internal.runners.ClassRoadie.runProtected(ClassRoadie.java:44)
	at org.junit.internal.runners.JUnit4ClassRunner.run(JUnit4ClassRunner.java:52)
	at org.apache.maven.surefire.junit4.JUnit4TestSet.execute(JUnit4TestSet.java:53)
	at org.apache.maven.surefire.junit4.JUnit4Provider.executeTestSet(JUnit4Provider.java:123)
	at org.apache.maven.surefire.junit4.JUnit4Provider.invoke(JUnit4Provider.java:104)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at org.apache.maven.surefire.util.ReflectionUtils.invokeMethodWithArray(ReflectionUtils.java:164)
	at org.apache.maven.surefire.booter.ProviderFactory$ProviderProxy.invoke(ProviderFactory.java:110)
	at org.apache.maven.surefire.booter.SurefireStarter.invokeProvider(SurefireStarter.java:175)
	at org.apache.maven.surefire.booter.SurefireStarter.runSuitesInProcessWhenForked(SurefireStarter.java:107)
	at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:68)

java.lang.AssertionError: expected:<16> but was:<1>
	at org.junit.Assert.fail(Assert.java:91)
	at org.junit.Assert.failNotEquals(Assert.java:645)
	at org.junit.Assert.assertEquals(Assert.java:126)
	at org.junit.Assert.assertEquals(Assert.java:470)
	at org.junit.Assert.assertEquals(Assert.java:454)
	at org.nuxeo.ecm.platform.pictures.tiles.service.test.TestService.testBorderTiles(TestService.java:416)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:601)
	at org.junit.internal.runners.TestMethod.invoke(TestMethod.java:66)
	at org.jmock.integration.junit4.JMock$1.invoke(JMock.java:37)
	at org.junit.internal.runners.MethodRoadie.runTestMethod(MethodRoadie.java:105)
	at org.junit.internal.runners.MethodRoadie$2.run(MethodRoadie.java:86)
	at org.junit.internal.runners.MethodRoadie.runBeforesThenTestThenAfters(MethodRoadie.java:94)
	at org.junit.internal.runners.MethodRoadie.runTest(MethodRoadie.java:84)
	at org.junit.internal.runners.MethodRoadie.run(MethodRoadie.java:49)
	at org.junit.internal.runners.JUnit4ClassRunner.invokeTestMethod(JUnit4ClassRunner.java:98)
	at org.junit.internal.runners.JUnit4ClassRunner.runMethods(JUnit4ClassRunner.java:61)
	at org.junit.internal.runners.JUnit4ClassRunner$1.run(JUnit4ClassRunner.java:54)
	at org.junit.internal.runners.ClassRoadie.runUnprotected(ClassRoadie.java:34)
	at org.junit.internal.runners.ClassRoadie.runProtected(ClassRoadie.java:44)
	at org.junit.internal.runners.JUnit4ClassRunner.run(JUnit4ClassRunner.java:52)
	at org.apache.maven.surefire.junit4.JUnit4TestSet.execute(JUnit4TestSet.java:53)
	at org.apache.maven.surefire.junit4.JUnit4Provider.executeTestSet(JUnit4Provider.java:123)
	at org.apache.maven.surefire.junit4.JUnit4Provider.invoke(JUnit4Provider.java:104)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:601)
	at org.apache.maven.surefire.util.ReflectionUtils.invokeMethodWithArray(ReflectionUtils.java:164)
	at org.apache.maven.surefire.booter.ProviderFactory$ProviderProxy.invoke(ProviderFactory.java:110)
	at org.apache.maven.surefire.booter.SurefireStarter.invokeProvider(SurefireStarter.java:175)
	at org.apache.maven.surefire.booter.SurefireStarter.runSuitesInProcessWhenForked(SurefireStarter.java:107)
	at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:68)