'Returns services formatted for consumption by f5-sdk update
The BIG-IP endpoint for services takes different values depending on
what you want the "allowed services" to be. It can be any of the
following
- a list containing "protocol:port" values
- the string "all"
- a null value, or None
This is a convenience function to massage the values the user has
supplied so that they are formatted in such a way that BIG-IP will
accept them and apply the specified policy.
:param services: The services to format. This is always a Python set
:return:'

def fmt_services(self, services):

    result = list(services)
    if (result[0] == 'all'):
        return 'all'
    elif (result[0] == 'none'):
        return None
    else:
        return list(services)
