Force JUnit 4 provider for Surefire

[INFO] --- maven-surefire-plugin:2.17:test (default-test) @ nuxeo-drive-operations ---
[INFO] Surefire report directory: /opt/jenkins/workspace/addons_nuxeo-drive-master/nuxeo-drive-server/nuxeo-drive-operations/target/surefire-reports

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running TestSuite
Configuring TestNG with: TestNGMapConfigurator
[TestNG] [ERROR] No test suite found. Nothing to run
(...)java.io.FileNotFoundException: /opt/jenkins/workspace/addons_nuxeo-drive-master/nuxeo-drive-server/nuxeo-drive-operations/target/surefire-reports/testng.css (No such file or directory)
	at java.io.FileOutputStream.open(Native Method)
	at java.io.FileOutputStream.<init>(FileOutputStream.java:221)
	at java.io.FileOutputStream.<init>(FileOutputStream.java:171)
	at org.testng.internal.Utils.writeResourceToFile(Utils.java:459)
	at org.testng.reporters.HtmlHelper.generateStylesheet(HtmlHelper.java:25)
	at org.testng.reporters.SuiteHTMLReporter.generateReport(SuiteHTMLReporter.java:48)
	at org.testng.TestNG.generateReports(TestNG.java:936)
	at org.testng.TestNG.run(TestNG.java:914)
	at org.apache.maven.surefire.testng.TestNGExecutor.run(TestNGExecutor.java:115)
	at org.apache.maven.surefire.testng.TestNGDirectoryTestSuite.executeMulti(TestNGDirectoryTestSuite.java:204)
	at org.apache.maven.surefire.testng.TestNGDirectoryTestSuite.execute(TestNGDirectoryTestSuite.java:107)
	at org.apache.maven.surefire.testng.TestNGProvider.invoke(TestNGProvider.java:112)
	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)
Configuring TestNG with: TestNGMapConfigurator
org.testng.TestNGException: 
Failure in JUnit mode for class org.nuxeo.drive.operations.TestGetChangeSummary: could not create/run JUnit test suite: 
Cannot find JUnit method class junit.framework.TestSuite$1.warning
	at org.testng.junit.JUnitTestRunner.runFailed(JUnitTestRunner.java:237)
	at org.testng.junit.JUnitTestRunner.start(JUnitTestRunner.java:230)
	at org.testng.junit.JUnitTestRunner.run(JUnitTestRunner.java:211)
	at org.testng.TestRunner$1.run(TestRunner.java:659)
	at org.testng.TestRunner.runWorkers(TestRunner.java:1147)
	at org.testng.TestRunner.privateRunJUnit(TestRunner.java:690)
	at org.testng.TestRunner.run(TestRunner.java:597)
	at org.testng.SuiteRunner.runTest(SuiteRunner.java:317)
	at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:312)
	at org.testng.SuiteRunner.privateRun(SuiteRunner.java:274)
	at org.testng.SuiteRunner.run(SuiteRunner.java:223)
	at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:52)
	at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:86)
	at org.testng.TestNG.runSuitesSequentially(TestNG.java:1039)
	at org.testng.TestNG.runSuitesLocally(TestNG.java:964)
	at org.testng.TestNG.run(TestNG.java:900)
	at org.apache.maven.surefire.testng.TestNGExecutor.run(TestNGExecutor.java:115)
	at org.apache.maven.surefire.testng.TestNGDirectoryTestSuite.executeMulti(TestNGDirectoryTestSuite.java:211)
	at org.apache.maven.surefire.testng.TestNGDirectoryTestSuite.execute(TestNGDirectoryTestSuite.java:107)
	at org.apache.maven.surefire.testng.TestNGProvider.invoke(TestNGProvider.java:112)
	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)