Location setting now updates summary timely.

Subscribed the LocationPreferenceController to listen to the location
providers changed action. This allows timely summary update. Previous
approach, directly calling the updateSummary method onResume failed in
the scenario when user changed the location settings via the
QuickSettings.

Test: Added robolectric tests, and manually verified the intended
behavior on a device.
Bug: 37956060
Change-Id: I2f81713d59da3384f3c98b327d377d529d440a88