salt-minion/Dockerfile.template: Keyword dev-python/libcloud-0.14.1

Avoiding:

  The following keyword changes are necessary to proceed:
   (see "package.accept_keywords" in the portage(5) man page for more details)
  # required by app-admin/salt-9999
  # required by =app-admin/salt-9999 (argument)
  =dev-python/libcloud-0.14.1 ~amd64