In case of constructing Client with session without specifying `retries`
value, `cinderclient.client.Client.retries` value become to None,
instead of 0. This raises TypeError on python 3 during comparison
`attempts > self.retries` on
`cinderclient.client.SessionClient._cs_request`
Closes-Bug: #1684787
Change-Id: If1ac36acb0d1c92e9779e3e8995606c9b34f2cde