Added Cancel button on DeviceAdminAdd.

Test: manual verification with KitchenSink
Test: atest --rebuild-module-info DeviceAdminAddCancelPreferenceControllerTest
Test: atest DeviceAdminAddWarningPreferenceControllerTest

Bug: 188585303

Change-Id: Ie48d72a605174775114802eb69c4dc0d5f1270ae
8 files changed