Apply sliding transition to trust agent.

- Also rename the extra of page transition.
- Remove useless code while starting activity from fragment.

Bug: 187542491
Test: robotest and manually went through trust agent flow.
Change-Id: I55419f23db7fa77281039e642bde5558c17dce0f

tests/robotests/src/com/android/settings/core/SubSettingLauncherTest.java

@@ -50,7 +50,6 @@ import org.robolectric.RobolectricTestRunner;
 import org.robolectric.RuntimeEnvironment;
 
 @RunWith(RobolectricTestRunner.class)
-@Config(shadows = ShadowUtils.class)
 public class SubSettingLauncherTest {
 
     @Mock
@@ -117,7 +116,6 @@ public class SubSettingLauncherTest {
 
     @Test
     public void launch_hasRequestListener_shouldStartActivityForResult() {
-        ShadowUtils.setIsPageTransitionEnabled(true);
         final int requestCode = 123123;
         when(mFragment.getActivity()).thenReturn(mActivity);