osd: EC Optimizations fix proc_master_log handling of splits

osd: EC Optimizations fix proc_master_log handling of splits

For optimized EC pools proc_master_log needs to deal with
the other log being merged being behind the local log because
it is missing partial writes. This is done by finding the
point where the logs diverge and then checking whether local
log entries have been committed on all the shards.

A bug in this code meant that after a PG split (where there
may be gaps in the log due to entries moving to the other PG)
that the divergence point was not found and committed
partial writes ended up being discarded which creates
unfound objects.

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