Convert LockscreenCredentialTest to JUnit4 am: 7d44e2f15c am: 2cbdc52f3c

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

Change-Id: I6cf32b196a4ccf768cd77ed0925a784196c7677c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>