Left timeutils and strutils in openstack/common since they are used in
openstack/common/apiclient and memorycache.

Change-Id: Idb5f09c159d907dfba84cd1f7501f650318af7d9

Connection Errors can be transient and there are many clients (including
auth_token middleware) that allow retrying requests that fail.

We should support this in the session, disabled by default, rather than
have multiple implementations for it.

For the moment I have purposefully not added it as an option to
Session.__init__ though I can see arguments for it. This can be added
later if there becomes a particular need.

I have also purposefully distinguished between Connection Errors (and
connect_retries) and HTTP errors. I don't know a good way to generalize
retrying on HTTP errors and they can be added later if required.

Blueprint: session-retries
Change-Id: Ia219636663980433ddb9c00c6df7c8477df4ef99

Provide access to get_token, get_endpoint and invalidate to the adapter.
The adapter is essentially created per individual client and it can be
useful to know things like the endpoint that requests will be sent to
based on the parameters that are included in the endpoint_filter.

This essentially allows us to emulate the management_url and auth_token
properties of the existing clients.

Change-Id: Ic01bc52bb38e8fb72e7a6d93bfd2944b11d0b070

The version parameter was left out of adapter previously because setting
a version number triggers discovery and I felt that it was not ready for
the other services.

However if it isn't set then it won't be used and we may as well
implement it here once rather than have the individual services that do
support it override it themselves.

Change-Id: I707380a01175dc19b59de32cbb8fd2bb123d7335

As much as I'd prefer not to need this functionality there are plenty of
existing clients that we want to have use the adapter that can accept a
bypass argument such that it ignores the service catalog and uses that
URL for all requests.

We therefore need to be able to support similar functionality in our
adapter.

Change-Id: I206705241ff9b84967d0d9c089b4795bcc26b65e

This is not technically needed, however we and the libraries we use,
aren't very good about keeping our strings and bytes straight for python
3. jsonutils has an attempt to decode stage that means we can let it
manage the correct types.

Change-Id: I2caf4a5b9a04495aa0286f2b6e3193a17ff246e5

A Session is a global object that can be shared around. There are
however many variables (those passed to session.request) that are
specific to the client that will be using that session. These often need
to be set for every request going through a client.

For this purpose we have a Session Adapter. An adapter is like a
view on a session. Where the session maintains very global state the
adapter maintains state relevant to a specific usage of a session. These
might be things like User-Agent which wants to be set per client using
the session, or possibly even auth plugins if we share a common session
object amongst a number of clients with different plugins.

Almost anything that gets passed to a Session.request() call is suitable
to go into an adapter (the exceptions are essentially the body data and
method which only makes sense per call)

Implements: blueprint session-propagation
Change-Id: I100c791806674213d3cdb5389d4b0a1cf88c82dd