osd: EC optimizations keep log entries on all shards

osd: EC optimizations keep log entries on all shards

When a shard is backfilling it gets given log entries
for partial writes even if they do not apply to the
shard. The code was updating the missing list but
discarding the log entry. This is wrong because the
update can be rolled backwards and the log entry is
required to revert the update to the missing list.
Keeping the log entry has a small but insignificant
performance impact.

Signed-off-by: Bill Scales <bill_scales@uk.ibm.com>
(cherry picked from commit 1fa5302092cbbb37357142d01ca008cae29d4f5e)