'Fetches the security group.
:returns: SecurityGroup object corresponding to sg_id'

@profiler.trace
def get(self, sg_id):

    secgroup = self.client.show_security_group(sg_id).get('security_group')
    sg_dict = self._sg_name_dict(sg_id, secgroup['security_group_rules'])
    return SecurityGroup(secgroup, sg_dict)
