Fix SetPolicyActivity finishing too early

CTS tests timeout if using: adb shell am start -W
This CL expands ag/10545042 to all SetPolicyActivity activities.
See origianl CL for full description.

Test: run cts -m CtsDevicePolicyManagerTestCases -t com.android.cts.devicepolicy.MixedDeviceOwnerTest#testSetWallpaper_disallowed

Bug: 149827369
Change-Id: Ib16e5239eced7bc9efdeae53b67c22cbdd2a63cc