Add getProfileOwnerNameUnchecked private method and use in manageUserUnchecked

Skip check for canManageUser.

Test: manual: download and install TestDPC
adb unroot && adb shell dpm set-device-owner --user 0 com.afwsamples.testdpc/.DeviceAdminReceiver
Fixes: 176107119

Change-Id: Ic00afaffc58a567490fa8fb3b8c66a9569e6333b