mds: enable optracker admin socket hooks

Signed-off-by: Greg Farnum <greg@inktank.com>
TrackedOp: create an "initiated" event on construction

This ensures we always have an event for state_string().

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

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

Signed-off-by: Greg Farnum <greg@inktank.com>
FIXUP MDS: add an OpTracker and use it

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