Hide lock_prefix argument using synchronized_with_prefix()

The lockfile module has a new convenience API which sets the lockfile prefix.
Using this API, the prefix is not required everytime synchronized is used.
This enables for projects to have consistant prefixes on their lockfiles

Change-Id: I4bc3f28a9ed2a6e2438a90f163bbde081211062c
Merge "Hide lock_prefix argument using synchronized_with_prefix()"