osd/PG: restrict async_recovery_targets to up osds

osd/PG: restrict async_recovery_targets to up osds

When an osd that is part of the acting set and not the up set, gets chosen
as an async_recovery_target, it gets removed from the acting set. Since this
osd is no longer in the up or acting set, it is classified as a stray in
the next peering cycle. This results in choose_acting() looping between two
proposed acting sets.

To avoid this, we will only choose up osds as async_recovery_targets.

Signed-off-by: Neha Ojha <nojha@redhat.com>