Fix random error on ITContextualActionsTest.verifyContextualActions

org.openqa.selenium.ElementNotVisibleException: Element is not currently visible and so may not be interacted with
Command duration or timeout: 27 milliseconds
Build info: version: '2.39.0', revision: '14fa800511cc5d66d426e08b0b2ab926c7ed7398', time: '2013-12-16 13:18:38'
System info: host: 'tweedledee', ip: '10.180.212.206', os.name: 'Windows Server 2008 R2', os.arch: 'amd64', os.version: '6.1', java.version: '1.8.0_31'
Driver info: org.openqa.selenium.firefox.FirefoxDriver
Capabilities [{applicationCacheEnabled=true, rotatable=false, handlesAlerts=true, databaseEnabled=true, version=26.0, platform=XP, browserConnectionEnabled=true, nativeEvents=false, acceptSslCerts=true, webStorageEnabled=true, locationContextEnabled=true, browserName=firefox, takesScreenshot=true, javascriptEnabled=true, cssSelectorsEnabled=true}]
Session ID: 3ae06521-ccbb-407b-9be3-1564924f84b4
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:408)
	at org.openqa.selenium.remote.ErrorHandler.createThrowable(ErrorHandler.java:193)
	at org.openqa.selenium.remote.ErrorHandler.throwIfResponseFailed(ErrorHandler.java:145)
	at org.openqa.selenium.remote.RemoteWebDriver.execute(RemoteWebDriver.java:554)
	at org.openqa.selenium.remote.RemoteWebElement.execute(RemoteWebElement.java:268)
	at org.openqa.selenium.remote.RemoteWebElement.click(RemoteWebElement.java:79)
	at sun.reflect.GeneratedMethodAccessor7.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:483)
	at org.openqa.selenium.support.pagefactory.internal.LocatingElementHandler.invoke(LocatingElementHandler.java:41)
	at com.sun.proxy.$Proxy13.click(Unknown Source)
	at org.nuxeo.functionaltests.pages.actions.ContextualActions.clickOnButton(ContextualActions.java:63)
	at org.nuxeo.ftest.cap.ITContextualActionsTest.verifyContextualActions(ITContextualActionsTest.java:103)
Caused by: org.openqa.selenium.remote.ErrorHandler$UnknownServerException: Element is not currently visible and so may not be interacted with
Build info: version: '2.39.0', revision: '14fa800511cc5d66d426e08b0b2ab926c7ed7398', time: '2013-12-16 13:18:38'
System info: host: 'tweedledee', ip: '10.180.212.206', os.name: 'Windows Server 2008 R2', os.arch: 'amd64', os.version: '6.1', java.version: '1.8.0_31'
Driver info: driver.version: unknown
	at <anonymous class&gt;.fxdriver.preconditions.visible(file:///C:/Users/nuxeo/AppData/Local/Temp/anonymous8793269813303225708webdriver-profile/extensions/fxdriver@googlecode.com/components/command_processor.js:8179)
	at <anonymous class&gt;.DelayedCommand.prototype.checkPreconditions_(file:///C:/Users/nuxeo/AppData/Local/Temp/anonymous8793269813303225708webdriver-profile/extensions/fxdriver@googlecode.com/components/command_processor.js:10814)
	at <anonymous class&gt;.DelayedCommand.prototype.executeInternal_/h(file:///C:/Users/nuxeo/AppData/Local/Temp/anonymous8793269813303225708webdriver-profile/extensions/fxdriver@googlecode.com/components/command_processor.js:10831)
	at <anonymous class&gt;.DelayedCommand.prototype.executeInternal_(file:///C:/Users/nuxeo/AppData/Local/Temp/anonymous8793269813303225708webdriver-profile/extensions/fxdriver@googlecode.com/components/command_processor.js:10836)
	at <anonymous class&gt;.DelayedCommand.prototype.execute/<(file:///C:/Users/nuxeo/AppData/Local/Temp/anonymous8793269813303225708webdriver-profile/extensions/fxdriver@googlecode.com/components/command_processor.js:10778)