rados: expand mon thrashing tests

- test sync (full and recent)
- test multiple mons down
- test other cluster sizes (3 and 9)

Signed-off-by: Sage Weil <sage@inktank.com>
(cherry picked from commit 5295406dbb0dd0c9ed07011d9f7d350e917c2149)
rados/monthrash: refactor a bit

Signed-off-by: Sage Weil <sage@inktank.com>
(cherry picked from commit dbf12a31aa02c73303e25ebc14b54bce3148c866)
rados/monthrash: reduce matrix size a bit

we don't need so many osd workloads
(cherry picked from commit 94ae48cf2c66939b4425f6c284ea25528c71d443)
rados/mon_thrash: inject random delays in mon messages

More useful than osd delays for this collection
(cherry picked from commit 0a13124c72b773948c823e200aaa87be1e5cae02)