Deduplicate adapter-of-installed-packages code.

Change-Id: I454ba79eddaaff86233a2cc341f4c8bebe94729e
Add some system packages to package list adapter.

As we're using the adapter for notification control stuff, we need to
include those packages, too, as they're throwing notifications as well.

Also optimize code a little.

Change-Id: I8829041a535923e3d93d9566e27eb99c48f25abd