Admin*LogPageActionTest: improve stability

[whipermr5]

These two tests always fail during the first test try, and sometimes fail all the way through all the test tries. The issue is caused by TestNG running the many*Logs test groups in a separate thread from the typical*Logs test groups. This results in an error as the LocalUserService used in GaeSimulation is not thread safe and throws an error when it is called from different threads.

The root issue lies with TestNG not honouring the specified parallel settings when the priority flag is set in the @Test annotation. There is a bug in the before/after mechanism that breaks the parallel feature (testng-team/testng#1185).

Workaround: either set singleThreaded = true on the test classes or drop the use of priority.

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Stack trace for AdminActivityLogPageActionTest:

java.lang.IllegalStateException: Operation not allowed in a thread that is neither the original request thread nor a thread created by ThreadManager
	at com.google.appengine.api.users.UserServiceImpl.getCurrentEnvironmentOrThrow(UserServiceImpl.java:152)
	at com.google.appengine.api.users.UserServiceImpl.getCurrentUser(UserServiceImpl.java:109)
	at teammates.logic.api.GateKeeper.getCurrentGoogleUser(GateKeeper.java:305)
	at teammates.logic.api.GateKeeper.getCurrentUser(GateKeeper.java:37)
	at teammates.ui.controller.Action.authenticateUser(Action.java:238)
	at teammates.ui.controller.Action.init(Action.java:98)
	at teammates.ui.controller.ActionFactory.getAction(ActionFactory.java:143)
	at teammates.test.driver.GaeSimulation.getActionObject(GaeSimulation.java:169)
	at teammates.test.cases.action.AdminActivityLogPageActionTest.getAction(AdminActivityLogPageActionTest.java:567)
	at teammates.test.cases.action.AdminActivityLogPageActionTest.statusMessageAndContinueSearch_withManyLogs_searchCorrectly(AdminActivityLogPageActionTest.java:390)
	...

Failed suite [Failed suite [Failed suite [ci-tests]]] > component-tests(failed)(failed)(failed) > teammates.test.cases.action.AdminActivityLogPageActionTest.statusMessageAndContinueSearch_withManyLogs_searchCorrectly FAILED
    java.lang.IllegalStateException at AdminActivityLogPageActionTest.java:567

Stack trace for AdminEmailLogPageActionTest:

java.lang.IllegalStateException: Operation not allowed in a thread that is neither the original request thread nor a thread created by ThreadManager
	at com.google.appengine.api.users.UserServiceImpl.getCurrentEnvironmentOrThrow(UserServiceImpl.java:152)
	at com.google.appengine.api.users.UserServiceImpl.getCurrentUser(UserServiceImpl.java:109)
	at teammates.logic.api.GateKeeper.getCurrentGoogleUser(GateKeeper.java:305)
	at teammates.logic.api.GateKeeper.getCurrentUser(GateKeeper.java:37)
	at teammates.ui.controller.Action.authenticateUser(Action.java:238)
	at teammates.ui.controller.Action.init(Action.java:98)
	at teammates.ui.controller.ActionFactory.getAction(ActionFactory.java:143)
	at teammates.test.driver.GaeSimulation.getActionObject(GaeSimulation.java:169)
	at teammates.test.cases.action.AdminEmailLogPageActionTest.getAction(AdminEmailLogPageActionTest.java:427)
	at teammates.test.cases.action.AdminEmailLogPageActionTest.statusMessageAndContinueSearch_withManyLogs_searchCorrectly(AdminEmailLogPageActionTest.java:291)
	...

Failed suite [Failed suite [Failed suite [ci-tests]]] > component-tests(failed)(failed)(failed) > teammates.test.cases.action.AdminEmailLogPageActionTest.statusMessageAndContinueSearch_withManyLogs_searchCorrectly FAILED
    java.lang.IllegalStateException at AdminEmailLogPageActionTest.java:427