sys user split: first pass updating Settings

Update various places in Settings to use "admin" ueser flag
instead of checking user id "0".  This should be no-op in
single user mode since the only admin user would be user 0.
In split system user mode, this will correctly ACL admin
user instead of non-interactive system user.

Bug: 19913735
Change-Id: Ida4d59c5f689ea0dc34b3b3ff0822b087fa0afd6

src/com/android/settings/ApnSettings.java

@@ -175,7 +175,7 @@ public class ApnSettings extends SettingsPreferenceFragment implements
         }
 
         if (mUm.hasUserRestriction(UserManager.DISALLOW_CONFIG_MOBILE_NETWORKS)
-                || UserHandle.myUserId()!= UserHandle.USER_OWNER) {
+                || !mUm.isAdminUser()) {
             mUnavailable = true;
             setPreferenceScreen(new PreferenceScreen(getActivity(), null));
             return;