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
diff --git a/src/com/android/settings/Utils.java b/src/com/android/settings/Utils.java
index 60973e1..84bb2dd 100644
--- a/src/com/android/settings/Utils.java
+++ b/src/com/android/settings/Utils.java
@@ -63,6 +63,7 @@
 import android.provider.ContactsContract.Data;
 import android.provider.ContactsContract.Profile;
 import android.provider.ContactsContract.RawContacts;
+import android.provider.Settings;
 import android.service.persistentdata.PersistentDataBlockManager;
 import android.support.v7.preference.Preference;
 import android.support.v7.preference.PreferenceGroup;
@@ -1100,5 +1101,10 @@
             }
         }
     }
+
+    public static boolean isDeviceProvisioned(Context context) {
+        return Settings.Global.getInt(context.getContentResolver(),
+                Settings.Global.DEVICE_PROVISIONED, 0) != 0;
+    }
 }