A few bug fixes:

- Fix incorrect ordering of arguments to the -f option.
  BTW, personally, I think using this format:

      -f <provider>.<function> [name1=value name2=value2 ...]

  makes more sense than the current format:

      -f <function> <provider> [name1=value name2=value2 ...]

  but anyways.

- Give better error message when -p <profile_name> is used but no instance
  names are supplied.

- Make ec2's list_node() also available for use with the -f option.

- Fix the incorrect assumption that a minion dict will always be
  available in the config when removing minion keys from master.
  It's possible that the node is a salt-master node created by the
  make_master option.