Fix random webdriver test error on ITUsersGroupsTest.testCreateSubGroupMember

org.openqa.selenium.TimeoutException: not loaded: null
Build info: version: '2.53.0', revision: '35ae25b1534ae328c771e0856c93e187490ca824', time: '2016-03-15 10:43:46'
System info: host: '3710d4dc0d89', ip: '172.17.0.9', os.name: 'Linux', os.arch: 'amd64', os.version: '4.4.0-87-generic', java.version: '1.8.0_77'
Driver info: driver.version: unknown
	at org.nuxeo.functionaltests.AbstractTest.fillElement(AbstractTest.java:383)
	at org.nuxeo.functionaltests.AbstractTest.asPage(AbstractTest.java:327)
	at org.nuxeo.functionaltests.pages.AbstractPage.asPage(AbstractPage.java:72)
	at org.nuxeo.functionaltests.pages.DocumentBasePage.getPermissionsTab(DocumentBasePage.java:300)
	at org.nuxeo.functionaltests.pages.DocumentBasePage.hasNewPermissionsButton(DocumentBasePage.java:735)
	at org.nuxeo.ftest.cap.ITUsersGroupsTest.testCreateSubGroupMember(ITUsersGroupsTest.java:216)
	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.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
	at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
	at org.nuxeo.functionaltests.LogTestWatchman$1.evaluate(LogTestWatchman.java:95)
	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.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
	at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
	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.openqa.selenium.TimeoutException: Timed out after 30 seconds waiting for org.nuxeo.functionaltests.AbstractTest$$Lambda$19/1379207867@3f628ce9
Build info: version: '2.53.0', revision: '35ae25b1534ae328c771e0856c93e187490ca824', time: '2016-03-15 10:43:46'
System info: host: '3710d4dc0d89', ip: '172.17.0.9', os.name: 'Linux', os.arch: 'amd64', os.version: '4.4.0-87-generic', java.version: '1.8.0_77'
Driver info: driver.version: unknown
	at org.openqa.selenium.support.ui.FluentWait.timeoutException(FluentWait.java:292)
	at org.openqa.selenium.support.ui.FluentWait.until(FluentWait.java:261)
	at org.nuxeo.functionaltests.AbstractTest.fillElement(AbstractTest.java:369)
	... 44 more