Make MasterClear a valid entry fragment.

Add FactoryResetActivity that maps to MasterClear fragment, and add
MasterClear to SettingsActivity's ENTRY_FRAGMENTS so that the
factory data reset fragment can be launched from activity alias.

Bug: 29405129
Change-Id: I8eca6b857987792da8d8678d33e6ab9d4e10793a

src/com/android/settings/SettingsActivity.java

@@ -352,6 +352,7 @@ public class SettingsActivity extends SettingsDrawerActivity
             TestingSettings.class.getName(),
             WifiAPITest.class.getName(),
             WifiInfo.class.getName(),
+            MasterClear.class.getName(),
     };