add upper_constraints support

- This change enforces the use of upper_constraints
  in tox envs.

Change-Id: I2badb5a3cd5f1ab2a66d3ebd97432b77985ada1b

tox.ini

@@ -7,9 +7,12 @@ skipsdist = True
 usedevelop = True
 install_command = pip install -U {opts} {packages}
 setenv =
-   VIRTUAL_ENV={envdir}
-deps = -r{toxinidir}/requirements.txt
-       -r{toxinidir}/test-requirements.txt
+  VIRTUAL_ENV={envdir}
+  CONSTRAINTS_OPT=-c {env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt}
+deps =
+  {env:CONSTRAINTS_OPT}
+  -r{toxinidir}/requirements.txt
+  -r{toxinidir}/test-requirements.txt
 whitelist_externals = bash
 commands = stestr run --black-regex ".tests.functional" {posargs}
 
@@ -21,6 +24,7 @@ commands = flake8
 basepython = python3
 commands = {posargs}
 deps =
+  {env:CONSTRAINTS_OPT}
   -r{toxinidir}/requirements.txt
   -r{toxinidir}/test-requirements.txt
   -r{toxinidir}/doc/requirements.txt
@@ -34,12 +38,16 @@ commands =
 
 [testenv:docs]
 basepython = python3
-deps = -r{toxinidir}/doc/requirements.txt
+deps =
+  {env:CONSTRAINTS_OPT}
+  -r{toxinidir}/doc/requirements.txt
 commands = sphinx-build -W doc/source doc/build
 
 [testenv:releasenotes]
 basepython = python3
-deps = -r{toxinidir}/doc/requirements.txt
+deps =
+  {env:CONSTRAINTS_OPT}
+  -r{toxinidir}/doc/requirements.txt
 commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:lower-constraints]