Update to 3.5.0

• Add LICENSE
• Add DOCS option
• Sort variables
• Reformat pkg-descr
• Update WWW
• While I'm here, allow concurrent installation (USE_PYTHON=concurrent)

Changes: https://docs.openstack.org/releasenotes/python-cinderclient/
PR: 228690
Submitted by: Kai <freebsd_ports@k-worx.org>
Approved by: Alexander Nusov <alexander.nusov@nfvexpress.com> (maintainer)