DO NOT MERGE: Use main looper for PackageMonitor

This is to work-around the issue that TvInputManagerService does not
receive package change callbacks from PackageMonitor.

In ATV emulator build, the background thread is blocked at
android_location_GpsLocationProvider_init(), and PackageMonitor that uses
background thread fails to handle broadcast intent.

Bug: 15767453
Change-Id: Ieef00cedf1357d57e4217ec202d50655ba3aa35a