Correctly save credential on config changes

Need to make a copy of the LockscreenCredential in
onSaveInstanceState() since the credential will be
zeroized in onDestroy() while Bundle.putParcelable()
only keeps a reference of the object without any
copying.

Bug: 179108398
Test: manual
Change-Id: I090b691630f82406d1ae2f625dd2e0d578b83707