Failing tests because of concurrency

[Zomis]

https://travis-ci.org/Cardshifter/Cardshifter/builds/37007190 and https://travis-ci.org/Cardshifter/Cardshifter/builds/37008087 failed because of some concurrency issues.

In the test it is possible for the AI to end turn at the same time as the human checks for what possible actions there are - which calls getCurrentPhase, which makes it possible for the LinkedList of upcomingPhases to be empty.

There are also some issues about wrong type of message received in the testUserOnlineOffline method