Fix issue #38210653: Few more tweaks of job scheduler

- Now keep track of the time a job was enqueued, and order
  the pending list by that.
- Added configuration constants for rescheduling: maximum
  times to reschedule, minimum backoff times.
- Fixed printing of active jobs -- the method to get the current
  JobStatus was old and didn't require the caller to hold a
  lock, so made a copy, which didn't contain all the data we were
  interested in.  Now with our simple locking, we can just make
  that require the caller hold a lock and return the real
  JobStatus object.
- Include oom_adj and procstate when printing information about
  processes being killed.
- Expanded documentation of BroadcastReceiver.goAsync().

Test: bit CtsJobSchedulerTestCases:*

Change-Id: I2e45f181e45be9836c74cbff1b844ffdf6e93019