Instead of automatically transitioning from PENDING to CONCLUDED, gate
the .prepare() and .commit() phases behind an explicit acknowledgement
provided by the QMP monitor if manual completion mode has been requested.
This allows us to perform graph changes in prepare and/or commit so that
graph changes do not occur autonomously without knowledge of the
controlling management layer.
Transactions that have reached the "PENDING" state together can all be
moved to invoke their finalization methods by issuing block_job_finalize
to any one job in the transaction.
Jobs in a transaction with mixed job->manual settings will remain stuck
in the "WAITING" state until block_job_finalize is authored on the job(s)
that have reached the "PENDING" state.
These jobs are not allowed to progress because other jobs in the
transaction may still fail during their preparation phase during
finalization, so these jobs must remain in the WAITING phase until
success is guaranteed. These jobs will then automatically dismiss
themselves, but jobs that had the manual property set will remain
at CONCLUDED as normal.