Update tox config

Update dependencies to include upper-constraints.

Change-Id: I7d9844b6b89bc0294ad4ed339f1fa63970ef037c

tox.ini

@@ -8,16 +8,22 @@ ignore_basepython_conflict = True
 basepython = python3
 usedevelop = True
 setenv = VIRTUAL_ENV={envdir}
-deps = -r{toxinidir}/requirements.txt
+deps =
+  -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+  -r{toxinidir}/requirements.txt
 
 [testenv:venv]
 commands = {posargs}
 
 [testenv:docs]
+deps =
+  -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+  -r{toxinidir}/requirements.txt
 commands =
   sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:pdf-docs]
+deps = {[testenv:docs]deps}
 envdir = {toxworkdir}/docs
 whitelist_externals =
   make