LockPatternView: set gesture exclusion on layout

- Otherwise, system gesture might be able to override the
  LockPatternView, causing MotionEvent to be pilfer-ed.

Test: http://shortn/_DlKHNocpVF
Bug: 290878374
Change-Id: I29901066c149fde434c8f91456e9d2e62d0a05e0
1 file changed