ENG-4278: Prep work.  Flip polarity of single-partition check, move it
above real code to remove an indentation level.
ENG-4278: Consolidate some end-of-transaction actions at the SPIs.
ENG-4278: Add R/O state to fragment task logging
ENG-4278: For read-only final fragment tasks:
1) Clear out SpScheduler outstanding txn state early so we won't
   generate CompleteTransactionTasks
2) Early complete and flush the MP transaction when done with a
   FragmentTask when appropriate.
Merge remote-tracking branch 'origin/master' into eng4278
Merge pull request #436 from VoltDB/eng4278

Eng4278
r=rbetts