Prevents users from being added if device is not provisioned

Also added a utility function for checking provisioning, instead of
repeating code for this check in several places.

bug:26156445
Change-Id: I9f4a280dd0cdf889f892e386dbf6a3fdb2a052ef

src/com/android/settings/DevelopmentSettings.java

@@ -339,9 +339,7 @@ public class DevelopmentSettings extends RestrictedSettingsFragment
         mWifiManager = (WifiManager) getSystemService(Context.WIFI_SERVICE);
 
         setIfOnlyAvailableForAdmins(true);
-        if (isUiRestricted()
-                || Settings.Global.getInt(getActivity().getContentResolver(),
-                        Settings.Global.DEVICE_PROVISIONED, 0) == 0) {
+        if (isUiRestricted() || !Utils.isDeviceProvisioned(getActivity())) {
             // Block access to developer options if the user is not the owner, if user policy
             // restricts it, or if the device has not been provisioned
             mUnavailable = true;