Hide soft keyboard when opening LockPatternActivity.

Due to the hidden EditText Views in this Activity, the soft keyboard
will open on some devices when opening this Activity. The keyboard
should be hidden by default so request this upon creating the Activity.

Change-Id: I1de09de4a58da002e0827c1f160cf7b76e020b9a
(cherry picked from commit 08584aaa)
(cherry picked from commit 5f3b778f)