Lock: delete untracked znodes if create_unique_znode fails to create an ephemeral znode for a lock.
Lock: delete untracked znodes if create_unique_znode fails to create an ephemeral znode for a lock.

Inside create_unique_znode, a znode creation request for a lock can fail with
an exception. It is needed to handle the exception and create new task for
deleting garbage znodes that incur deadlock.

Reviewed-by: Kirill Pinchuk <3553f40fba3159aa620e3b5a91d3ea1e5c845d22@gmail.com>

tipsi/aiozk,tipsi/aiozk