WorkQueue: add TPHandle to allow _process to ping the hb map

Backport: bobtail
Signed-off-by: Samuel Just <sam.just@inktank.com>
OSD: use TPHandle in peering_wq

Implement _process overload with TPHandle argument and use
that to ping the hb map between pgs and between map epochs
when advancing a pg.  The thread will still timeout if
genuinely stuck at any point.

Fixes: 3905
Backport: bobtail
Signed-off-by: Samuel Just <sam.just@inktank.com>
FileStore: ping TPHandle after each operation in _do_transactions

Each completed operation in the transaction proves thread
liveness, a stuck thread should still trigger the timeouts.

Fixes: #3928
Backport: bobtail
Signed-off-by: Samuel Just <sam.just@inktank.com>