DPMS setDeviceOwner access control

* Check whether the caller is system or has
  permission to set the device owner before
  checking whether the package exists on
  device.

Manual testing
* Call DPMS setDeviceOwner with an installed
  package but not as the system caller
* Call DPMS setDeviceOwner with an uninstalled
  package and not as the system caller
* Both calls should give the same error message
  and logs.

Bug: 184525740
Test: manual testing
      atest com.android.server.devicepolicy.DevicePolicyManagerTest
      atest com.android.cts.devicepolicy.DeviceOwnerTest
Change-Id: I5654ef420ff44af01d475595609bb85fec132ce1