Update consumer static membership fencing system test to support new protocol

consumer_test.py contains OffsetValidationTest.test_fencing_static_consumer that verifies the sequence in which static members join a group when using conflicting instance id. This behaviour is different in the classic and consumer protocol, so the tests should be updated to set the right expectations when running with the new consumer protocol. Note that what the tests covers (params, setup), apply to both protocols. It is the expected results that are not the same.

When conflicts between static members joining a group:

Classic protocol: all members join the group with the same group instance id, and then the first one will eventually receive a HB error with FencedInstanceIdException

Consumer protocol: new member with an instance Id already in use is not able to join, receiving an UnreleasedInstanceIdException in the response to the HB to join the group.