ReplicatedPG: always take recovery_read_lock for recovery

Signed-off-by: Samuel Just <sjust@redhat.com>
osd/: update peer_missing and local missing if we write a degraded object

Signed-off-by: Samuel Just <sjust@redhat.com>
osd/: don't block writes on degraded objects

Signed-off-by: Samuel Just <sjust@redhat.com>