Summary:
Failure to create the lock file (e.g. out of space) could
prevent future LockFile attempts in the same process on the same file
from succeeding.

Also added DEBUG code to fail assertion if PosixFileLock is destroyed
without using UnlockFile (which is a risk because FileLock is in the
public API with virtual destructor).

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8747

Test Plan: test added

Reviewed By: ajkr

Differential Revision: D30732543

Pulled By: pdillinger

fbshipit-source-id: 4c30a959566d91f778d6fad3fbbd5f3941b097c1