Print services setting changes not handled for managed profiles.

We keep per user settings for enabled print services which are
observed to update the print manager service state. We were listening
to all user changes but the handling code was not updating the state
of the user whose settings changed, rather the current user.

Added hidden APIs in content observer to know which user changed
and now the print manager serivce handles content changes for the
correct user.

bug:16977006

Change-Id: I71ec88c8f3f38cb405844c13ab83695c2029eb79