Don't use a query for watch_rule_get()

When getting a database record by ID, it is much more efficient to get() it
directly than to perform a query or the database to obtain the ID (again)
and then get it.

Change-Id: I89b46d698c033e54ee9a50172ccad3eb3833cb1e
Merge "Don't use a query for watch_rule_get()"