Use DevicePolicyData#mUserSetupComplete for DPM's isDeviceProvisioned.

DevicePolicyData#mUserSetupComplete on user 0 us a more accurate and
reliable indicator of whether the device has been provisioned than
the currently used 'ro.device_owner' property.

Test: gts-tradefed run gts -m GtsGmscoreHostTestCases --test com.google.android.gts.devicepolicy.DevicePolicyManagerTest

BUG: 29935702

Change-Id: Iec62f2aebe865ac0ee69c2cc7177333ce5450474