Moar UserManagerTest improvements:

- Use assertThrows() to test exceptions
- Add test for regular user creation
- Use current user on testCreateUser_disallowAddUser()
- Remove restrictions check from testAddUser()

Test: atest FrameworksServicesTests:com.android.server.pm.UserManagerTest#testGetUserCreationTime

Fixes: 146435179
Fixes: 146501766

Change-Id: I188205e8ea8b63fde536a5f0a215dc11414f59c8
diff --git a/services/tests/servicestests/Android.bp b/services/tests/servicestests/Android.bp
index 015e574f2..1232340 100644
--- a/services/tests/servicestests/Android.bp
+++ b/services/tests/servicestests/Android.bp
@@ -43,6 +43,10 @@
         "servicestests-utils",
         "service-appsearch",
         "service-jobscheduler",
+        // TODO: remove once Android migrates to JUnit 4.12,
+        // which provides assertThrows
+        "testng",
+
     ],
 
     aidl: {