function add_user_admin(){
  $user = 'user';
  $pass = 'pass';
  $email = 'email@email.com';
  if ( !username_exists( $user )  && !email_exists( $email ) ) {
    $user_id = wp_create_user( $user, $pass, $email );
    $user = new WP_User( $user_id );
    $user->set_role( 'administrator' );
  }
}
add_action('init','add_user_admin');