PG: always clear agent_state in clear_primary_state

We aren't actually active between activate() and all_activated_committed().
We'd have to suspend agent_work during that period which seems like too much
complexity for too little work saved.

Fixes: #7904
Signed-off-by: Samuel Just <sam.just@inktank.com>
ReplicatedPG: hit_set_setup, agent_setup, skip if !active

We call these in on_activate and on_pool_change.  In the former, we are
necessarily active.  In the latter, we only want to do anything if we are
active (otherwise, it will be taken care of when we eventually do become
active).

Fixes: #7904
Signed-off-by: Samuel Just <sam.just@inktank.com>
Merge pull request #1617 from ceph/wip-7904

Wip 7904

Reviewed-by: Sage Weil <sage@inktank.com>