Handle deferred deletion race condition

[kiran pawar]

In deferred deletion shares, consider below scenario

00:00: do_deferred_share_deletion runs
00:01: do_deferred_snapshot_deletion runs
00:02 snapshot A of share B gets deleted and put into deferred_deleting
00:03: share B gets deleted and put into deferred_deleting
00:05: do_deferred_share_deletion runs: snapshot A still existing !
00:06: do_deferred_snapshot_deletion runs

We must make sure all snapshot instance are deleted first, before deleting share instance in deferred deletion scenario.
Also, once share will be deferred deleted and error occurred, it should be handled either by manila automatically or by admin only, i.e. end user should never see that share. That means, all errors in deferred_deleting should go to only error_deferred_deleting.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/manila/+/921313