ENH: fix to use upstream --remove-rules

https://fedorahosted.org/firewalld/ticket/10
DOC: document required firewalld version as > 0.3.7.1
firewalld-0.3.8 release that support --remove-rules out so documenting this.
Merge pull request #412 from grooverdan/firewalld

ENH: enhance firewall-cmd to use firewall-0.8.3's --remove-rules