Add possibility to allow ICMP traffic inside firewall-rules

VMs cannot answer to 'ping' by default, because firewall rule for ICMP traffic is not set.
With this pull request I modified **--fw-rules** option in order to be able to set ICMP traffic firewall rule also.
Now choosing **protocol** is mandatory, while **start** and **end** port must be used only with tcp and udp protocols.
If ICMP is enabled, by design only ECHO, ECHO REPLY and DESTINATION UNREACHABLE (only codes 0,1) types are allowed:
 * http://www.iana.org/assignments/icmp-parameters/icmp-parameters.xml