Add tox job to build docs

This commit adds a tox job to build the docs. It calls the setup.py
build_sphinx command.

Change-Id: I84dbd1aaea142bbe45c73df04856e128621143db
Change of copyright to HP for keystone regions

Modified copyight header from "OpenStack Foundation" to
"Hewlett-Packard Development Company, L.P" as the following files
were submitted by  Hewlett-Packard Development Company according to the
review link https://review.openstack.org/#/c/93347/

tempest/api/identity/admin/v3/test_regions.py
tempest/services/identity/v3/json/region_client.py
tempest/services/identity/v3/xml/region_client.py

Change-Id: Id6ff2717d882b165636f010590d00dd2ebb4e184
Merge "Change of copyright to HP for keystone regions"
Merge "Add tox job to build docs"