Implement action bar back button in voicemail PIN settings

Previously the VoicemailChangePinActivity does not have the parent
activity set in the manifest or other implementations so the back
button does nothing.

The same behavior of the navigation bar back is used.

Change-Id: Ia16a754063bb72e5796c8d3ebf193e63613cf001
Fixes: 31634760
1 file changed