Add an intent extra to force master clear

Currently, if a priv-app sends ACTION_MASTER_CLEAR, whilst
DISALLOW_FACTORY_RESET is set, the factory reset is blocked. This CL
introduces a new extra for master clear that let's the priv-app bypass
the user restriction.

Bug: 28689894
Change-Id: I4bf979a3826454e977f1abff4562f85c8d0eec4a