Fix layout-demo tests using mongo database

org.openqa.selenium.TimeoutException: not loaded: overviewTabLink
Build info: version: '2.53.0', revision: '35ae25b', time: '2016-03-15 17:00:58'
System info: host: '0fed86061ccc', ip: '172.17.0.5', os.name: 'Linux', os.arch: 'amd64', os.version: '4.4.0-62-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)
	at org.nuxeo.functionaltests.AbstractTest.asPage(AbstractTest.java:327)
	at org.nuxeo.functionaltests.AbstractTest.get(AbstractTest.java:286)
	at org.nuxeo.ftest.formsLayoutDemo.AbstractWidgetPageTest.navigateTo(AbstractWidgetPageTest.java:51)
	at org.nuxeo.ftest.formsLayoutDemo.ITSelectOneDirectoryWidgetTest.testWidget(ITSelectOneDirectoryWidgetTest.java:3

Unable to locate element: {"method":"xpath","selector":"//form[@id='selectOneRadioDirectoryWidgetLayout_view_form']/table/tbody/tr/td[2]"}
Command duration or timeout: 215 milliseconds
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: '0fed86061ccc', ip: '172.17.0.5', os.name: 'Linux', os.arch: 'amd64', os.version: '4.4.0-62-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: 063dac37-9766-4550-a054-554b19b6c532
*** Element info: {Using=xpath, value=//form[@id='selectOneRadioDirectoryWidgetLayout_view_form']/table/tbody/tr/td[2]}

Caused by: java.lang.IllegalArgumentException: Can't put a null key for the cache 'cache-layout_demo_crew'!
	at org.nuxeo.ecm.core.cache.CacheAttributesChecker.put(CacheAttributesChecker.java:66)
	at org.nuxeo.ecm.core.cache.CacheWrapper.put(CacheWrapper.java:70)
	at org.nuxeo.ecm.core.cache.CacheMetrics.put(CacheMetrics.java:117)
	at org.nuxeo.ecm.directory.DirectoryCache.getEntry(DirectoryCache.java:123)
	at org.nuxeo.directory.mongodb.MongoDBSession.getEntry(MongoDBSession.java:123)
	at org.nuxeo.directory.mongodb.MongoDBSession.getEntry(MongoDBSession.java:115)
	at org.nuxeo.ecm.platform.ui.web.directory.DirectoryHelper.getEntryThrows(DirectoryHelper.java:215)
	at org.nuxeo.ecm.platform.ui.web.directory.DirectoryHelper.getEntry(DirectoryHelper.java:230)
	at org.nuxeo.ecm.platform.ui.web.directory.DirectoryEntryOutputRenderer.getEntryLabel(DirectoryEntryOutputRenderer.java:114)
	at org.nuxeo.ecm.platform.ui.web.directory.DirectoryEntryOutputRenderer.encodeBegin(DirectoryEntryOutputRenderer.java:57)