Fix 'jobscheduler run' shell command

Tidying up the locking + deferred-work shape of the job scheduler's
internal flow inadvertently meant that we were now trying to bind to
a job service while under the shell user's uid when the relevant
shell command was used to kick off the job.  Now we don't do that.

Bug 37744607
Test: manual

Change-Id: Ia4b83f83f9fbd2e5678eaa279f1d86206fb05023