Convert LockscreenCredentialTest to JUnit4 am: 7d44e2f15c

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/2775374

Change-Id: I63fca8979d84c0ced0ebc9f804c94b7e53a22ee9
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>