osd/osd_types: add eversion_t to hit_set_info_t

Track the eversion stamp on the hit_set objects we've written.  This makes
life a bit easier later when we need to generate log entries and don't
want to bother stating the objects.

Signed-off-by: Sage Weil <sage@inktank.com>
osd/ReplicatedPG: track version on hit_set objects we've written

Signed-off-by: Sage Weil <sage@inktank.com>
osd/ReplicatedPG: trim old hit_set objects on persist

Any time we persist a hit_set object, take the opportunity to remove any
old ones that we don't want any more.

Note that this means if the admin decreases the number of objects to track,
we won't remove them until the next time we persist something.  We also
don't clean up if the HitSet tracking is disabled entirely.

Signed-off-by: Sage Weil <sage@inktank.com>
ceph_test_rados: hit hit_set_{list,get} rados operations

This will do a list, and then get a random HitSet.

Signed-off-by: Sage Weil <sage@inktank.com>