Ignore the interruption of the stop operation - will finish asynchronously.
Remove redundant `ocf_queue_put`.
Move creating the `finish_thread` during the cache stop
from the `_cache_mngt_cache_stop_sync` to the `cache_mngt_exit_instance`
and give it a proper handling.
Signed-off-by: Slawomir Jankowski <slawomir.jankowski@intel.com>