fix 2517656 Pin/Password Unlocks place focus on the launcher screen when they shouldn't

PasswordEntryKeyboardHelper now sets the FLAG_KEEP_TOUCH_MODE flag for the events
so that the last event we process from the soft keybaord doesn't exit touch mode
and we don't erroneously go into non-touch mode since the on-screen button pressing
left us in touch mode.

Change-Id: Id2546ec3bc4b337aedb5e925de0c709ce62ea059