Prior to this patch, novaclient was handling sessions in an inconsistent
manner.

Every time we created a client instance, it would use a global
connection pool, which made it difficult to use in a process that is
meant to be forked.

Obviously sessions like the ones provided by the requests library that
will automatically cause connections to be kept alive should not be
implicit. This patch moves the novaclient back to the age of a single
session-less request call by default, but also adds two more
resource-reuse friendly options that a user needs to be explicit about.

The first one is that both v1_1 and v3 clients can now be used as
context managers,. where the session will be kept open (and thus the
connection kept-alive) for the duration of the with block. This is far
more ideal for a web worker use-case as the session can be made
request-long.

The second one is the per-instance session. This is very similar to what
we had up until now, except it is not a global object so forking is
possible as long as each child instantiates it's own client. The session
once created will be kept open for the duration of the client object
lifetime.

Please note: client instances are not thread safe. As can be seen from
above forking example - if you wish to use threading/multiprocessing,
you *must not* share client instances.

DocImpact

Related-bug: #1247056
Closes-Bug: #1297796
Co-authored-by: Nikola Dipanov <ndipanov@redhat.com>
Change-Id: Id59e48f61bb3f3c6223302355c849e1e99673410

Conflicts:
	novaclient/client.py
	novaclient/tests/test_client.py
	novaclient/tests/test_http.py
	novaclient/v1_1/client.py
	novaclient/v3/client.py

Currently when booting a server with V3, novaclient sends an empty
os_password to image_cs. This will cause 401(Unauthorized: Invalid
user/password) when trying to find image. This is is a result of
changes nova's V3 API: nova is no longer used as a proxy for the
image service. So novaclient uses two Client instances: one for
nova, the other for image service. This patch checks os_password
before creating the image Client and assigns it if it's empty.

Change-Id: Ic54cef93e9b823fb98b1edd78776c9a1fc06ba46
Closes-Bug: #1277425

CLI support for blueprint instance-group-api-extension

REST API support:- https://review.openstack.org/#/c/62557/

DocImpact
 - supports create, list, get and delete
 - only V2 is supported

Change-Id: Iaa5a2922b9a0eed9f682b7584c2acf582379b422

servers.Server represents various object now, and some of them may
don't have attribute 'name', for example, the interface_list() result
object. It will cause AttributeError when we try to format string with
such object, so I add a check for the 'name' attribute in __repr__
method, it will use 'unknown-name' instead when 'name' is not found.

Change-Id: If4757d5d73721774543d58a4cc875710a6013f34
Closes-Bug: #1280453

Currently, "nova server-group-delete" can only delete one server
group in one request, this patch was enabling nova client support
removing multiple server groups in one request.

Change-Id: I373151bc27cbe8617e2023ba99f6fb3f0108d592
Closes-Bug: #1302954

Conflicts:
	novaclient/tests/v1_1/test_shell.py