Convert LockscreenCredentialTest to JUnit4

Convert LockscreenCredentialTest from the JUnit3-based AndroidTestCase,
which is deprecated, to JUnit4.

Bug: 219511761
Bug: 232900169
Bug: 243881358
Test: atest LockscreenCredentialTest
Change-Id: Id8da1606b1f758ff91f67c25d37a36f36a72c2bf
Merged-In: Id8da1606b1f758ff91f67c25d37a36f36a72c2bf
(cherry picked from commit b63430f2dae18fc34adf8cd2949906e8937d851f)
1 file changed