Fix FT ITCommentTest with MySQL

org.openqa.selenium.NoSuchElementException: Unable to locate element: {"method":"xpath","selector":"//textarea"}
Command duration or timeout: 396 milliseconds
For documentation on this error, please visit: http://seleniumhq.org/exceptions/no_such_element.html
Build info: version: '2.53.0', revision: '35ae25b1534ae328c771e0856c93e187490ca824', time: '2016-03-15 10:43:46'
System info: host: '9486949d6810', ip: '172.17.0.11', os.name: 'Linux', os.arch: 'amd64', os.version: '4.4.0-96-generic', java.version: '1.8.0_77'
Driver info: org.openqa.selenium.firefox.FirefoxDriver
Capabilities [{applicationCacheEnabled=true, rotatable=false, handlesAlerts=true, databaseEnabled=true, version=42.0, platform=LINUX, nativeEvents=false, acceptSslCerts=true, webStorageEnabled=true, locationContextEnabled=true, browserName=firefox, takesScreenshot=true, javascriptEnabled=true, cssSelectorsEnabled=true}]
Session ID: 110d5721-9896-4d17-af23-393f72c97013
*** Element info: {Using=xpath, value=//textarea}
	at sun.reflect.GeneratedConstructorAccessor25.newInstance(Unknown Source)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
	at org.openqa.selenium.remote.ErrorHandler.createThrowable(ErrorHandler.java:206)
	at org.openqa.selenium.remote.ErrorHandler.throwIfResponseFailed(ErrorHandler.java:158)
	at org.openqa.selenium.remote.RemoteWebDriver.execute(RemoteWebDriver.java:678)
	at org.openqa.selenium.remote.RemoteWebDriver.findElement(RemoteWebDriver.java:363)
	at org.openqa.selenium.remote.RemoteWebDriver.findElementByXPath(RemoteWebDriver.java:500)
	at org.openqa.selenium.By$ByXPath.findElement(By.java:361)
	at org.openqa.selenium.remote.RemoteWebDriver.findElement(RemoteWebDriver.java:355)
	at org.openqa.selenium.support.pagefactory.DefaultElementLocator.findElement(DefaultElementLocator.java:69)
	at org.openqa.selenium.support.pagefactory.internal.LocatingElementHandler.invoke(LocatingElementHandler.java:38)
	at com.sun.proxy.$Proxy41.clear(Unknown Source)
	at org.nuxeo.functionaltests.pages.tabs.CommentsTabSubPage.addComment(CommentsTabSubPage.java:70)
	at org.nuxeo.functionaltests.pages.tabs.CommentsTabSubPage.addComment(CommentsTabSubPage.java:61)
	at org.nuxeo.ftest.cap.ITCommentTest.testReplyToComment(ITCommentTest.java:90)
Caused by: org.openqa.selenium.NoSuchElementException: Unable to locate element: {"method":"xpath","selector":"//textarea"}
For documentation on this error, please visit: http://seleniumhq.org/exceptions/no_such_element.html
Build info: version: '2.53.0', revision: '35ae25b1534ae328c771e0856c93e187490ca824', time: '2016-03-15 10:43:46'
System info: host: '9486949d6810', ip: '172.17.0.11', os.name: 'Linux', os.arch: 'amd64', os.version: '4.4.0-96-generic', java.version: '1.8.0_77'
Driver info: driver.version: unknown
	at <anonymous class>.FirefoxDriver.prototype.findElementInternal_(file:///tmp/anonymous7939965131794025284webdriver-profile/extensions/fxdriver@googlecode.com/components/driver-component.js:10770)
	at <anonymous class>.fxdriver.Timer.prototype.setTimeout/<.notify(file:///tmp/anonymous7939965131794025284webdriver-profile/extensions/fxdriver@googlecode.com/components/driver-component.js:625)