SQUASH OSD: scan for dropped PGs in consume_map instead of advance_map

We have to wait until after we know that nobody will be adding ops for
newly-dead PGs to the list. While we're moving it, switch the locking
so we only hold a write lock while deleting the actual lists.

Signed-off-by: Greg Farnum <greg@inktank.com>
SQUASH: enqueue_op no longer requires holding the osd_lock.
SQUASH OSD: move the {boot,up,bind} epochs into OSDService

Provide interfaces around setting and retrieving them, instead of accessing
them directly with a lock.

Signed-off-by: Greg Farnum <greg@inktank.com>
OSD: move the peer_epoch infrastructure into OSDService

Signed-off-by: Greg Farnum <greg@inktank.com>
OSD: move build_incremental_map_msg into OSDService

Signed-off-by: Greg Farnum <greg@inktank.com>
OSD: Move send_map into OSDService

Signed-off-by: Greg Farnum <greg@inktank.com>
OSD: Move send_incremental_map into OSDService

Signed-off-by: Greg Farnum <greg@inktank.com>
OSD: move _share_map_outgoing into OSDService

Signed-off-by: Greg Farnum <greg@inktank.com>
OSD: rename share_map_incoming and share_map_outgoing

share_map_incoming -> share_map
share_map_outgoing -> share_map_peer

Signed-off-by: Greg Farnum <greg@inktank.com>