Fix locking bug

When lock_path is not set, lockutils creates a new temp dir for
each new call to synchronized.  This results in no actual lock
enforcement.  Require setting of lock_path by throwing an
exception if it is not found.

Fixes bug 1065531
Fixes bug 1162047

Change-Id: I178684a1d8649b5bcfcb768be0a68c8efa3f00e4
Merge "Fix locking bug"