Add an other-requirements.txt file containing a cross-platform list
of dependencies needed for running included tox-based tests. Also
include a tox environment for convenience calling the bindep[*]
utility to list any missing system requirements.
This change is self-testing.
For other-requirements.txt see also
http://docs.openstack.org/infra/manual/drivers.html#package-requirements
Update pbr constraints so that pep8 passes
[*] http://docs.openstack.org/infra/bindep/
Change-Id: Ic976b8924d965bd8e2ad3216db0355389e102afc