osd: make last state for slow requests more informative

Report on the last event string, and pass in important context for the
op event list, including:

 - which peers were sent sub ops and we are waiting for
 - which pg queue we are delayed by

Signed-off-by: Sage Weil <sage@inktank.com>
osd: show last few events for slow requests

Signed-off-by: Sage Weil <sage@inktank.com>
Revert "osd: show last few events for slow requests"

This reverts commit c78c3a1b20f0f128033e1a615e50c0c82ce0b61c.
better