'Create a network/VPC
:param      cidr_block: The CIDR block assigned to the network
:type       cidr_block: ``str``
:param      name: An optional name for the network
:type       name: ``str``
:param      instance_tenancy: The allowed tenancy of instances launched
into the VPC.
Valid values: default/dedicated
:type       instance_tenancy: ``str``
:return:    Dictionary of network properties
:rtype:     ``dict``'

def ex_create_network(self, cidr_block, name=None, instance_tenancy='default'):

    params = {'Action': 'CreateVpc', 'CidrBlock': cidr_block, 'InstanceTenancy': instance_tenancy}
    response = self.connection.request(self.path, params=params).object
    element = response.findall(fixxpath(xpath='vpc', namespace=NAMESPACE))[0]
    network = self._to_network(element, name)
    if (name and self.ex_create_tags(network, {'Name': name})):
        network.extra['tags']['Name'] = name
    return network
