OSD: introduce require_up_osd_peer() function for gating replica ops

This checks both that a Message originates from an OSD, and that the OSD
is up in the given map epoch.
We use it in handle_replica_op so that we don't inadvertently add operations
from down peers, who might or might not know it.

Signed-off-by: Greg Farnum <greg@inktank.com>
(cherry picked from commit ccd0eec50103b919b3eb6eea96f7dc6438520ed3)
OSD: use OpRequestRef& for a few require_* functions

Signed-off-by: Greg Farnum <greg@inktank.com>
(cherry picked from commit eb2f1ea2c33647934af878b504383829f5a198ce)
OSD: introduce require_self_aliveness(OpRequestRef&,epoch_t) function

Take the self-aliveness checks out of require_same_or_newer_map() and use
the new function for that and for require_up_osd_peer().

Signed-off-by: Greg Farnum <greg@inktank.com>
(cherry picked from commit e179e9227b4a4482d8359682092fd7f426b9a919)
OSD: add require_same_peer_inst(OpRequestRef&,OSDMap&) helper

Signed-off-by: Greg Farnum <greg@inktank.com>
(cherry picked from commit e99acf9810976b1fc74b84ad289773af43be973f)
Merge branch 'next'

Conflicts:
	src/osd/OSD.cc