osd/ReplicatedPG: drop RepGather::ondone callback

We kick the blocked contexts in the completion path of process_copy_chunk(),
after we have take the RWWRITE obc lock.  There is no need to delay the
unblocking until the RepGather finishes.

This also fixes a leak: the ondone wasn't getting cleaned up if a peering
interval change happens and the repgather is applied early in on_change().

Signed-off-by: Sage Weil <sage@inktank.com>
osd/ReplicatedPG: fix promote cancellation

The canceling caller cleans up the blocked objects for us; we simply need
to bail out early.

Signed-off-by: Sage Weil <sage@inktank.com>
ceph-kvstore-tool: optional output filename for get

Signed-off-by: Sage Weil <sage@inktank.com>