Lock screen should not display password.

Bug 3179062

Problem was introduced in CL 78854: changing the keyListener should not
change the transformation method.

mInputType changes are brittle. It is often reset to TYPE_CLASS_TEXT or to
mInput.getInputType(). The TYPE_TEXT_FLAG_MULTI_LINE and TYPE_TEXT_VARIATION_PASSWORD
variation are then added back based on the previous state. But this is not consistent,
and sometimes, only one of those is set.

This should be refactored if a bug is found in what seems to work correclty at the moment.

Change-Id: Ie251ec7db0ce0af4a07564b0dbb53465e6f361c6