Remove unused class SequentialRejoinCoordinator and its tests.
Add elastic join usage to VoltDB's command line help message.
Refactor ClusterConfig.addPartitions() to use guava's multimap for parameter.
Remove elastic join specific methods from JoinCoordinator base class.
ENG-4622: Add ElasticJoinService interface.
ENG-4622: Instantiate and run elastic join coordinator as a service on all
nodes.
Cache exception in StreamSnapshotDataTarget for checking later.
Demote StreamSnapshotDataTarget initialization message to debug.
ENG-4622: Move generic snapshot response handler from JoinCoordinator to
SnapshotUtils.
Merge branch 'master' into ENG-4622

Removed:
	tests/frontend/org/voltdb/rejoin/TestIv2RejoinCoordinator.java
	tests/frontend/org/voltdb/rejoin/TestIv2RejoinCoordinatorLive.java
ENG-5094: Refactor SimpleClientResponseAdapter to allow setting callback.

This makes it easier to have different callbacks for different transactions with
the same adapter.
txnid2: add mpratio workload mix option
ENG-4622: Only instantiate the elastic service when elastic is enabled in pro.
Merge branch 'master' into ENG-4622-5094
Merge branch 'master' into ENG-4622-5094
Fix LeaderAppointer check for elastic.

Taking the coward way out of this. Loosing the partition count check on
LeaderAppointer promotion. If a new LeaderAppointer is elected, only crash if
the number of partitions is LESS than that when the cluster initially
started. Elastic join adds new partitions on the fly, so tolerate that.
ENG-4622: Allow setting timeout on the SimpleClientResponseAdapter's sync
callback.
ENG-4962: Introduce MpTransactionTaskQueue, subclassed from
TransactionTaskQueue.  Use it in place of TransactionTaskQueue in the
MPI.
ENG-4962: SP transaction task queue doesn't need the repair() method.
ENG-4962: Can get rid of this stuff