osd: EC optimizations fix bug when recovering only partial write objects

osd: EC optimizations fix bug when recovering only partial write objects

PGLog::reset_complete_to is not handling the scenario where all the
missing objects have a partial write that excludes updating the shard being
recovered as their most recent update. In this scenario the oldest need
is newer than newest log entry. Setting last_compelte to the head of the
log confuses code and makes it think that recovery has completed.

The fix is to hold last_complete one entry behind the head of the log
until all missing objects have been recovered.

PGLog::recover_got already does this when an object is recovered and the
remaining objects to recover match this scenario, so this fix just makes
reset_complete_to behave the same way as recover_got.

Signed-off-by: Bill Scales <bill_scales@uk.ibm.com>