Add a recovery callback to destroy partially-recovered members
when interrupted by failure

Fix the case of one rank finishing a store where its partner
fails, followed by a commit on the succesfull rank. Now come to
a consensus on timestamps on group reinitialization.

…lize

More thought can be put in to this (e.g. if a rank has failed, but all remaining
ranks reach finalize, could we just finalize anyway?)

Possible when a rank fails after reaching finalize if the remaining ranks
inconsistently succeed/fail on the barrier finishing.