RadosClient: Fixing potential lock leaks.

In lookup_pool and pool_delete, a lock is taken
before invoking wait_for_osdmap, but is not
released for the failure case of the call. Fixing the same.

Fixes: #9022
Signed-off-by: Pavan Rallabhandi <pavan.rallabhandi@sandisk.com>
Merge pull request #2220 from somnathr/wip-lock-leak-fix

RadosClient: Fixing potential lock leaks.

Backport: firefly
Reviewed-by: Sage Weil <sage@redhat.com>