OSK can render above the greeter before password prompt

[Brandon Schaefer]

To reproduce, you'll need to compile/install this libertine branch:
https://code.launchpad.net/~brandontschaefer/libertine/enable-maliit

From test out gedit on a libertine branch. Ensure this is with xmir:2:1.17.2-1ubuntu0.1~overlay11. A higher version will fix the focusing of the xmir apps.

On a vivid+overlay phone updated with:
- Open gedit, ensure the OSK opens.
- Lock phone
- Attempt to unlock.

Expect:
  Normal greeter with no osk open

Result:
  OSK open over the greeter and the OSK sending input to gedit.