Added '--fw-rules' option to implement createFirewallRule API

This option implements createFirewallRule API when called with <tt>knife cs server create</tt> command.

Ref.
http://cloudstack.apache.org/docs/api/apidocs-4.0.0/root_admin/createFirewallRule.html

For us it is very useful because we need to automate creation of chef nodes on cloudstack with static_nat enabled and we would like to set firewall policies for static public ip during VM creation.