Fix FT failure in ITCoverageNavigationTest

org.openqa.selenium.TimeoutException: Timed out after 30 seconds waiting for org.nuxeo.functionaltests.Locator$10@a4b2d8f
Build info: version: '2.53.0', revision: '35ae25b', time: '2016-03-15 17:00:58'
System info: host: '75d94dd904ec', ip: '172.17.0.9', os.name: 'Linux', os.arch: 'amd64', os.version: '4.4.0-98-generic', java.version: '1.8.0_77'
Driver info: driver.version: unknown
	at sun.reflect.GeneratedConstructorAccessor13.newInstance(Unknown Source)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
	at org.openqa.selenium.remote.ErrorHandler.createThrowable(ErrorHandler.java:206)
	at org.openqa.selenium.remote.ErrorHandler.throwIfResponseFailed(ErrorHandler.java:158)
	at org.openqa.selenium.remote.RemoteWebDriver.execute(RemoteWebDriver.java:678)
	at org.openqa.selenium.remote.RemoteWebDriver.findElement(RemoteWebDriver.java:363)
	at org.openqa.selenium.remote.RemoteWebDriver.findElementByLinkText(RemoteWebDriver.java:428)
	at org.openqa.selenium.By$ByLinkText.findElement(By.java:246)
	at org.openqa.selenium.remote.RemoteWebDriver.findElement(RemoteWebDriver.java:355)
	at org.nuxeo.functionaltests.Locator$10.apply(Locator.java:417)
	at org.nuxeo.functionaltests.Locator$10.apply(Locator.java:414)
	at org.openqa.selenium.support.ui.FluentWait.until(FluentWait.java:238)
	at org.nuxeo.functionaltests.Locator.waitUntilElementPresent(Locator.java:414)
	at org.nuxeo.functionaltests.ITCoverageNavigationTest.testCoverageNavigation(ITCoverageNavigationTest.java:88)
Caused by: org.openqa.selenium.NoSuchElementException: Unable to locate element: {"method":"link text","selector":"Africa"}
For documentation on this error, please visit: http://seleniumhq.org/exceptions/no_such_element.html
Build info: version: '2.53.0', revision: '35ae25b', time: '2016-03-15 17:00:58'
System info: host: '75d94dd904ec', ip: '172.17.0.9', os.name: 'Linux', os.arch: 'amd64', os.version: '4.4.0-98-generic', java.version: '1.8.0_77'
Driver info: driver.version: unknown
	at <anonymous class>.FirefoxDriver.prototype.findElementInternal_(file:///tmp/anonymous8541115715227837984webdriver-profile/extensions/fxdriver@googlecode.com/components/driver-component.js:10770)
	at <anonymous class>.fxdriver.Timer.prototype.setTimeout/<.notify(file:///tmp/anonymous8541115715227837984webdriver-profile/extensions/fxdriver@googlecode.com/components/driver-component.js:625)