Reduce app size by downgrading inactive apps

This will trigger when the device will have low space.
Active apps here refer to the apps which were either active
in foregrond or in background and also used by other packages.
Apps which are inactive for X days downgraded to verify. X is
determined by sysprop pm.dexopt.unopt_after_inactive_days

If the system properties are not set, no effect will take place.

The above operations will take place in background dexopt service.
If user uses the app again, it will again be speed-compiled when
background dexopt service starts next time.

Bug: 36598475
Test: manual
* Remove the check in the code that allows downgrade only when
  the space is low on the device.
* adb root
* Set pm.dexopt_unopt_after_inactive_days to 600
* Make sure the current time of the device is correctly set
* Install 2 non system apps - B, C
* Downgrade B to extract
* Upgrade a system apps to speed-profile - E
* Downgrade a system app to quicken - G
* adb shell cmd package bg-dexopt-job

Expected Results:
* Extract - B
* Verify - C
* There should not be any entries for apps E an G
  in dalvik_cache

Change-Id: I68f9f617d6722a7ba8b00aa2181cb38a165cfc51