Prepare for local/remote admin users

Local admins are the ones accessing MaxScale on the same host
over a Unix domain socket, and who are strongly identified), and
optional remote admins are the ones accessing MaxScale potentially
over a tcp socket (potentially over the network), and who are
weakly identified.

These are completely separate and a different set of functions
will be needed for managing them. This initial change merely
renames the functions.

server/modules/authenticator/max_admin_auth.c

@@ -142,7 +142,7 @@ max_admin_auth_set_protocol_data(DCB *dcb, GWBUF *buf)
         dcb->data = (void *)session_data;
 
         /* Check for existance of the user */
-        if (admin_search_user(session_data->user))
+        if (admin_local_search_user(session_data->user))
         {
             session_data->validated = true;
             return 0;