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: remove a couple leftover declarations of MDRequest

Signed-off-by: Greg Farnum <greg@inktank.com>
MDCache: pass the causative message to request_start_slave()

We were passing the causative MDS (as an int), but pushing down the
actual Message will help us as we set up an OpTracker.

Signed-off-by: Greg Farnum <greg@inktank.com>
MDS: add stubs for an AdminSocketHook

Signed-off-by: Greg Farnum <greg@inktank.com>
Mutation: add an MDRequestParams struct and use that when building MDRequests

We now have a single constructor and one path to build MDRequests with.

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

Signed-off-by: Greg Farnum <greg@inktank.com>
MDCache: mark ops at various finish points

Signed-off-by: Greg Farnum <greg@inktank.com>
Server: mark events when journaling and replying

Signed-off-by: Greg Farnum <greg@inktank.com>
Locker: mark_event in acquire_locks() when blocking or succeeding

Signed-off-by: Greg Farnum <greg@inktank.com>
mds: add a Server::submit_mdlog_entry() to provide event marking

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