Fix off-by-one error in mw.track subscriber

For mw.track( 'event.foo' ), it would try to load
'schema..foo'.

Also listen for 'event.' instead of 'event', in case
someone decides to use 'events.' or 'eventually.'
or whatever.

Bug: 72197
Change-Id: Idb7db8dfa12d24955ea8d51d7280f9438f8b87a7
Merge "Fix off-by-one error in mw.track subscriber"