'Locate service group with given port.
Return virtualServers (vs) entry whose port matches the
supplied parameter port. For a negative port, just return
the first vs entry.
None is returned if no match found.
:param lb: Softlayer loadbalancer model.
:type lb: ``dict``
:param port: loadbalancer front-end port.
:type port: ``int``
:return: Matched entry in the virtualServers array of the supplied
model.
:rtype: ``dict``'

def _locate_service_group(self, lb, port):

    vs = None
    if (port < 0):
        vs = (lb['virtualServers'][0] if lb['virtualServers'] else None)
    else:
        vs = find(lb['virtualServers'], (lambda v: (v['port'] == port)))
    return vs
