Add tests for libuserdefs

*** 12,19 ****
  #
  # Copyright (c) 2012 by Delphix. All rights reserved.
  # Copyright 2014 Garrett D'Amore <garrett@damore.org>
  #
  
! SUBDIRS = dis dladm iconv libnvpair_json printf xargs
  
  include $(SRC)/test/Makefile.com
--- 12,19 ----
  #
  # Copyright (c) 2012 by Delphix. All rights reserved.
  # Copyright 2014 Garrett D'Amore <garrett@damore.org>
  #
  
! SUBDIRS = dis dladm iconv libnvpair_json libuserdefs printf xargs
  
  include $(SRC)/test/Makefile.com