Fix PermissionSubPage loading problems

org.openqa.selenium.TimeoutException: Timed out after 30 seconds waiting for org.nuxeo.functionaltests.pages.tabs.PermissionsSubPage$$Lambda$19/215690645@6415f61e
Build info: version: '2.53.0', revision: '35ae25b1534ae328c771e0856c93e187490ca824', time: '2016-03-15 10:43:46'
System info: host: 'jabba5', ip: '172.17.0.7', os.name: 'Linux', os.arch: 'amd64', os.version: '4.4.0-22-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.Locator.waitUntilGivenFunctionIgnoring(Locator.java:485)
	at org.nuxeo.functionaltests.Locator.waitUntilGivenFunction(Locator.java:443)
	at org.nuxeo.functionaltests.pages.tabs.PermissionsSubPage.waitForPermissionAdded(PermissionsSubPage.java:135)
	at org.nuxeo.functionaltests.pages.tabs.PermissionsSubPage.grantPermission(PermissionsSubPage.java:129)
	at org.nuxeo.ftest.cap.ITCollectionsTest.testRightsOnCollection(ITCollectionsTest.java:264)

org.openqa.selenium.StaleElementReferenceException: Element is no longer attached to the DOM
Command duration or timeout: 6 milliseconds
For documentation on this error, please visit: http://seleniumhq.org/exceptions/stale_element_reference.html
Build info: version: '2.53.0', revision: '35ae25b1534ae328c771e0856c93e187490ca824', time: '2016-03-15 10:43:46'
System info: host: 'oldjoyeux', ip: '10.213.0.35', os.name: 'Linux', os.arch: 'amd64', os.version: '3.13.0-74-generic', java.version: '1.8.0_60'
Driver info: org.openqa.selenium.firefox.FirefoxDriver
Capabilities [{applicationCacheEnabled=true, rotatable=false, handlesAlerts=true, databaseEnabled=true, version=26.0, platform=LINUX, browserConnectionEnabled=true, nativeEvents=false, acceptSslCerts=true, webStorageEnabled=true, locationContextEnabled=true, browserName=firefox, takesScreenshot=true, javascriptEnabled=true, cssSelectorsEnabled=true}]
Session ID: 51d6fa4f-15cb-4d22-86ce-5ac00fd63753
*** Element info: {Using=xpath, value=.//span[contains(@class, 'tag')]}
	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:422)
	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.RemoteWebElement.execute(RemoteWebElement.java:327)
	at org.openqa.selenium.remote.RemoteWebElement.findElements(RemoteWebElement.java:214)
	at org.openqa.selenium.remote.RemoteWebElement.findElementsByXPath(RemoteWebElement.java:299)
	at org.openqa.selenium.By$ByXPath.findElements(By.java:356)
	at org.openqa.selenium.remote.RemoteWebElement.findElements(RemoteWebElement.java:190)
	at org.nuxeo.functionaltests.pages.tabs.PermissionsSubPage.hasPermission(PermissionsSubPage.java:73)
	at org.nuxeo.ftest.cap.ITPermissionsTest.testPermissionsOn(ITPermissionsTest.java:244)
	at org.nuxeo.ftest.cap.ITPermissionsTest.testWorkspacePermissions(ITPermissionsTest.java:149)
Caused by: org.openqa.selenium.StaleElementReferenceException: Element is no longer attached to the DOM
For documentation on this error, please visit: http://seleniumhq.org/exceptions/stale_element_reference.html
Build info: version: '2.53.0', revision: '35ae25b1534ae328c771e0856c93e187490ca824', time: '2016-03-15 10:43:46'
System info: host: 'oldjoyeux', ip: '10.213.0.35', os.name: 'Linux', os.arch: 'amd64', os.version: '3.13.0-74-generic', java.version: '1.8.0_60'
Driver info: driver.version: unknown
	at <anonymous class&gt;.fxdriver.cache.getElementAt(resource://fxdriver/modules/web-element-cache.js:9457)
	at <anonymous class&gt;.Utils.getElementAt(file:///tmp/anonymous38849410649634321webdriver-profile/extensions/fxdriver@googlecode.com/components/driver-component.js:9039)
	at <anonymous class&gt;.FirefoxDriver.prototype.findElementsInternal_(file:///tmp/anonymous38849410649634321webdriver-profile/extensions/fxdriver@googlecode.com/components/driver-component.js:10788)
	at <anonymous class&gt;.FirefoxDriver.prototype.findChildElements(file:///tmp/anonymous38849410649634321webdriver-profile/extensions/fxdriver@googlecode.com/components/driver-component.js:10809)
	at <anonymous class&gt;.DelayedCommand.prototype.executeInternal_/h(file:///tmp/anonymous38849410649634321webdriver-profile/extensions/fxdriver@googlecode.com/components/command-processor.js:12661)
	at <anonymous class&gt;.DelayedCommand.prototype.executeInternal_(file:///tmp/anonymous38849410649634321webdriver-profile/extensions/fxdriver@googlecode.com/components/command-processor.js:12666)
	at <anonymous class&gt;.DelayedCommand.prototype.execute/<(file:///tmp/anonymous38849410649634321webdriver-profile/extensions/fxdriver@googlecode.com/components/command-processor.js:12608)