OpTracker: use mark_event rather than _mark_event

mark_event() interfaced changed to accept time and it is default
to 'now'. The mark_event is the wrapper function of _mark_event()
and it has the check for optracking enabled/disabled as well.
The _mark_event() is now a private function.

Signed-off-by: Somnath Roy <somnath.roy@sandisk.com>
OpTracker: The optracker enabled/disabled check is added

The optracker enabled/disabled check is now added in the
mark_event(const string&) interface.

Signed-off-by: Somnath Roy <somnath.roy@sandisk.com>
ReplicatedPG: Removed the redundant register_snapset_context call

In the get_object_context(), the get_snapset_context is been called
and the register_snapset_context is already been invoked from there.
This call seems to be redundant.

Signed-off-by: Somnath Roy <somnath.roy@sandisk.com>
OSD: adjust share_map() to handle the case that the osd is down

The assert was hitting while OSd is waiting for becoming healthy
in handle_osd_map(). This can happen while io is going on and
OSDs are made down forcefully by say osd thrash command.
So, the fix could be instead of asserting just return from here.

Fixes: http://tracker.ceph.com/issues/8646

Signed-off-by: Somnath Roy <somnath.roy@sandisk.com>
Merge remote-tracking branches 'origin/wip-8691', 'origin/wip-7891', 'upstream/next', 'somnathr/wip-sd-share-map', 'somnathr/wip-sd-replicated-pg' and 'somnathr/wip-sd-optracker' into wip-sam-testing2