Settings ChooseLockscreen* dismiss in background.

Whenever launching
ChooseLockGeneric/ChooseLockPassword/ChooseLockPassword the activity
will finish itself when it goes into the background. This is to ensure
that a user only has an opporunity to complete this process once the
activity is shown. (It cannot be resumed after a power button press, or
sending the activity to the background)

Test: Verified in Settings that the ChooseLockGeneric,
ChooseLockPassword and the ChooseLockPattern activities now exit if they
are sent to the background.
Test: Same as above but in SUW
Test: m -j40 RunSettingsRoboTests ROBOTEST_FILTER=com.android.settings.password.ChooseLockPatternTest
Test: m -j40 RunSettingsRoboTests ROBOTEST_FILTER=com.android.settings.password.ChooseLockPasswordTest
Fixes: 287473148

Change-Id: Icc9142ff4672ab3669b2f425ff351b03ce7a223a