Use tempdir for lock_path in tests.

Commit: 2331d3336a6adf4fc13a3b187e91a5d1b1f7c723
introduced use of lockutils but wasn't setting a lock_path, in the tests.
As a result we were polluting cinder/openstack/ with cinder-xxxx lockfiles.

This patch adds a tempfile and cleanup to the test so we don't leave any
junk behind.

Change-Id: Idd9fee928ff0fcf3f8d1c30ee88c5306b88e290c
Merge "Use tempdir for lock_path in tests."