Merge "Add Constraints support"

tox.ini

@@ -7,7 +7,7 @@ envlist = py35,py34,py27,pep8,pypy
 usedevelop=True
 whitelist_externals = find
                       rm
-install_command = pip install -U {opts} {packages}
+install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} {opts} {packages}
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 passenv = http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY