When using `use_max` or `use_min` in `pam_limits`, the new value is an integer compared with the actual_value which is a string, so they are always different and the module reports a changed but none occurred.
Early pam_limits module didn't support special values for items.
This patch is adding support to special values unlimited, infinity and -1.
Issue: https://github.com/ansible/ansible-modules-extras/issues/1033
Signed-off-by: Ondra Machacek <machacek.ondra@gmail.com>