osd: EC Optimizations: Peer changes for partial logs

osd: EC Optimizations: Peer changes for partial logs

Changes to peering for replica/strays to handle partial
logs. For EC optimized pools shards may not have a complete
log if there have been partial writes that did not update
the shard. If the most recent entries in the log have all
skipped updating a shard then it will have a log that ends
earlier than other shards. During peering the primary which
has a full copy of the log works out whether other shards
have any missing objects and then communicates this to
the replica/stray shards during activation.

The primary uses the partial write last complete data in
pg_info_t to explain to other shards if they are missing
log entries and just need to update last_update and
last_complete.

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