Prevent clickjacking of superuser requests

Enable filterTouchesWhenObscured on the accept request button to prevent
possible clickjacking attacks. This is a measure used in many sensitive
dialogs (app installation, backup & VPN) in AOSP.

Change-Id: I33c18c449c909b97b29b981bffe7f3095adee506
Merge remote-tracking branch 'cm/cm-11.0' into omni-4.4