The version class allows us to parse, and compare, API version strings
as per the OpenStack API WG Microversion Specification. Several formats
are supported:
* v#.#.# (legacy)
* #.#.# (legacy)
* [service name] #.#.#
In the former two cases, a service type will have to be manually supplied
to ensure proper comparison.
https://specs.openstack.org/openstack/api-wg/guidelines/microversion_specification.html
Change-Id: If3596418dfe2e76489bdb48d4d15f7f3e7a6d2f9