Added processing /compute URL for getting list of versions

After implementing blueprint "Ability to run some Nova services under Apache2"(
https://blueprints.launchpad.net/nova/+spec/run-nova-services-under-apache2)
it becomes possible not to use separate ports for each openstack service but
share 80 port with different URL prefixes.

Mailing list thread with discussion the details of this feature:
http://lists.openstack.org/pipermail/openstack-dev/2015-June/067147.html.

Openstack wiki page with mapping urls to services:
https://wiki.openstack.org/wiki/URLs.

If nova-api service is started by Apache (or similar),
using 'Alias' directive script name contains alias-prefix.
We get things like: '/ALIAS/NAME/v2', '/ALIAS/NAME/v2.1'
This change makes sure we compose correct url for getting list of versions.

Co-Authored-By: Marian Horban <mhorban@mirantis.com>
Co-Authored-By: Pavel Kholkin <pkholkin@mirantis.com>

Closes-Bug: #1471833

Change-Id: I2c78e22095975aef777bc62b19d46bcc8fea2d96
4 files changed