Convert firewall rule allowed user-string to specified REST API format.

def _parse_allow(allow):
    '''
    Convert firewall rule allowed user-string to specified REST API format.
    '''
    # input=> tcp:53,tcp:80,tcp:443,icmp,tcp:4201,udp:53
    # output<= [
    #     {"IPProtocol": "tcp", "ports": ["53","80","443","4201"]},
    #     {"IPProtocol": "icmp"},
    #     {"IPProtocol": "udp", "ports": ["53"]},
    # ]
    seen_protos = {}
    allow_dict = []
    protocols = allow.split(',')
    for p in protocols:
        pairs = p.split(':')
        if pairs[0].lower() not in ['tcp', 'udp', 'icmp']:
            raise SaltCloudSystemExit(
                'Unsupported protocol {0}. Must be tcp, udp, or icmp.'.format(
                    pairs[0]
                )
            )
        if len(pairs) == 1 or pairs[0].lower() == 'icmp':
            seen_protos[pairs[0]] = []
        else:
            if pairs[0] not in seen_protos:
                seen_protos[pairs[0]] = [pairs[1]]
            else:
                seen_protos[pairs[0]].append(pairs[1])
    for k in seen_protos:
        d = {'IPProtocol': k}
        if seen_protos[k]:
            d['ports'] = seen_protos[k]
        allow_dict.append(d)
    log.debug("firewall allowed protocols/ports: %s", allow_dict)
    return allow_dict