Fix tests and compiler warnings

- Added an additional check to make sure the testMessageBus doesn't refer to a different
messageBus set by previous test that also uses AbstractSinglenode test.
For instance, if RabbitSingle node tests run before
RedisSingle node tests and Rabbit wasn't available, the Redis tests still use
Rabbit message bus that was set by the AbstractSingleNode test class.
Since the TestSupportResource is evaluated after the testmessagebus
is set, adding this check is needed.

- Fixed compiler warnings