nest nodegroup match in nodegroups file

fix issue #12700
so we can use nest nodegroups in config
https://groups.google.com/forum/?fromgroups=#!topic/salt-users/xtnsqiadupk
for example
nodegroups:
  web: 'E@(server1,server2)'
  db: 'E@(server3, server4)'
  production: 'N@web,N@db'
  preproduction: 'L@server5'