After testing, it seems that the K8s API servers can get blocked for an
indeterminate period during tests - a period that can be longer than the
10 seconds in which our GameServer goes from Ready->Reserverd->Ready -
which caused the previous version of the test to fail.

Updated the test to only look at the event stream to ensure the e2e test
state is verified. While it would be ideal to look at the state itself,
we will assume that unit tests cover that the Event stream is accurate
to the GameServer state being changed.

Fixes googleforgames#1276