Fix issue #27920133: Need to ensure activity starts in idle maintenance

We now hold a wake lock while going in to idle maintenance, since
we really want to make sure everyone has a chance to respond.  And
since we are doing that, we can move to just using a delayed message
to make sure we don't leave maintenance until the time expires, getting
rid of the separate timeout alarm.

Also improve the initial transition to light idle mode so that if
we currently have work going on, we will wait for up to 15 minutes
more before actually going idle and forcing it to stop.

Change-Id: I6045da57ab4165f80a651126e99371c029ced23d