Incorrect concatenation in the version discovery

[s10]

urllib.parse.urljoin in Cinder version discovery generates wrong version URLs.

How to reproduce:
1. Start Cinder API behind the proxy, pass headers X-Forwarded-For, X-Forwarded-Proto, X-Forwarded-Prefix (/volume)
2. Enable proxy headers parsing in the http_proxy_to_wsgi middleware:
[oslo_middleware]
enable_proxy_headers_parsing=True

Expected result
===============
https://api.example.com/volume/v3/ in the version discovery responses.

Actual result
=============
$ curl https://api.example.com/volume
{"versions": [{"status": "DEPRECATED", "updated": "2017-02-25T12:00:00Z", "links": [{"href": "https://docs.openstack.org/", "type": "text/html", "rel": "describedby"}, {"href": "https://api.example.com/v2/", "rel": "self"}], "min_version": "", "version": "", "media-types": [{"base": "application/json", "type": "application/vnd.openstack.volume+json;version=2"}], "id": "v2.0"}, {"status": "CURRENT", "updated": "2017-09-19T20:18:14Z", "links": [{"href": "https://docs.openstack.org/", "type": "text/html", "rel": "describedby"}, {"href": "https://api.example.com/v3/", "rel": "self"}], "min_version": "3.0", "version": "3.50", "media-types": [{"base": "application/json", "type": "application/vnd.openstack.volume+json;version=3"}], "id": "v3.0"}]}

Environment
===========
OpenStack Pike (at least), Queens, Rocky.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/630085
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=175aaa879d8b940d800e1b96e8871bd350798038
Submitter: Zuul
Branch: master

commit 175aaa879d8b940d800e1b96e8871bd350798038
Author: zhurong <email address hidden>
Date: Fri Jan 11 16:30:01 2019 +0800

    Fix version return incorrect when endpoint url end without /

    when request to cinder endpoint url end without /
    $ curl http://127.0.0.1/volume
    the version herf return incorrect, like below:
    "href": "http://127.0.0.1/v2/"
    "href": "http://127.0.0.1/v3/"
    This patch will always add a '/' to the endpoint url end.

    Closes-bug: #1816793
    Change-Id: I6b0f47fc5b11c44a767e0ebfe2929e560c5f5432

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/rocky
Review: https://review.openstack.org/638387

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/queens
Review: https://review.openstack.org/638389

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/638387
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=48d188c78af52696b90fb9e90d823b56e7429ab3
Submitter: Zuul
Branch: stable/rocky

commit 48d188c78af52696b90fb9e90d823b56e7429ab3
Author: zhurong <email address hidden>
Date: Fri Jan 11 16:30:01 2019 +0800

    Fix version return incorrect when endpoint url end without /

    when request to cinder endpoint url end without /
    $ curl http://127.0.0.1/volume
    the version href return incorrect, like below:
    "href": "http://127.0.0.1/v2/"
    "href": "http://127.0.0.1/v3/"
    This patch will always add a '/' to the endpoint url end.

    Closes-bug: #1816793
    Change-Id: I6b0f47fc5b11c44a767e0ebfe2929e560c5f5432
    (cherry picked from commit 175aaa879d8b940d800e1b96e8871bd350798038)

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/638389
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=309f72202d0c76b7b4be3ca96327a8b784a1bc69
Submitter: Zuul
Branch: stable/queens

commit 309f72202d0c76b7b4be3ca96327a8b784a1bc69
Author: zhurong <email address hidden>
Date: Fri Jan 11 16:30:01 2019 +0800

    Fix version return incorrect when endpoint url end without /

    when request to cinder endpoint url end without /
    $ curl http://127.0.0.1/volume
    the version href return incorrect, like below:
    "href": "http://127.0.0.1/v2/"
    "href": "http://127.0.0.1/v3/"
    This patch will always add a '/' to the endpoint url end.

    Closes-bug: #1816793
    Change-Id: I6b0f47fc5b11c44a767e0ebfe2929e560c5f5432
    (cherry picked from commit 175aaa879d8b940d800e1b96e8871bd350798038)

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/cinder 14.0.0.0rc1 release candidate.

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/cinder 13.0.4 release.

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/cinder 12.0.6 release.