KeyguardInputTests: Check lock screen availability

OEMs are allowed not to implement lock screen, so all lock screen
related tests should check lock screen availability and return
assumption failure when the device doesn't have one.

Test: atest KeyguardInputTests
Bug: 162288726
Change-Id: I58d553ace3d549947d8a9db6cdcde729de460d04
(cherry picked from commit 09dc99e8804528123d5640e6099dd6a791cb1f09)
1 file changed