osd: EC Optimizations proc_master_log bug fixes

osd: EC Optimizations proc_master_log bug fixes

1. proc_master_log can roll forward full-writes that have
been applied to all shards but not yet completed. Add a
new function consider_adjusting_pwlc to roll-forward
pwlc. Later partial_write can be called to process the
same writes again. This can result in pwlc being rolled
backwards. Modify partial_write so it does not undo pwlc.

2. At the end of proc_master_log we want the new
authorative view of pwlc to persist - this may be
better or worse than the stale view of pwlc held by
other shards. consider_rollback_pwlc sometimes
updated the epoch in the toversion (second value of the
range fromversion-toverison). We now always do this.
Updating toversion.epoch causes problems because this
version sometimes gets copied to last_update and
last_complete - using the wrong epoch here messes
everything up in later peering cycles. Instead we
now update fromversion.epoch. This requires changes
to apply_pwlc and an assert in Stray::react(const MInfoRec&)

3. Calling apply_pwlc at the end of proc_master_log is
too early - updating last_update and last_complete here
breaks GetMissing. We need to do this later when activating
(change to search_missing and activate)

4. proc_master_log is calling partial_write with the
wrong previous version - this causes problems after a
split when the log is sparsely populated.

5. merging PGs is not setting up pwlc correctly which
can cause issues in future peering cycles. The
pwlc can simply be reset, we need to update the epoch
to make sure this view of pwlc persists vs stale
pwlc from other shards.

Signed-off-by: Bill Scales <bill_scales@uk.ibm.com>
(cherry picked from commit 0b8593a0112e31705acb581ac388a4ef1df31b4b)