Add 'shell cmd jobscheduler run ....' to run a job immediately

During development one needs to be able to test changes conveniently,
and when the jobs would normally have hard-to-simulate constraints
like idle-time or long minimum latencies, testing becomes difficult.
This CL introduces the ability to run a specific job immediately
from the adb shell.

Without the "-f"/"--force" flag, the job still won't run if it has
unmet "functional" requirements such as being connected via an
unmetered network.  With that flag, the job will be run immediately
regardless of its declared constraints (so it may not work properly
due to lack of network connectivity or similar).

Bug 27501783

Change-Id: Icc046f53f8846690c8234e60066e85c283d325ce