Use constraints in tox.ini

As per email [1] from Andreas, we can add upper constraints on packages
used now.

[1] http://openstack.markmail.org/thread/a4l7tokbotwqvuoh

Change-Id: Iaaacbac9d931a9deb3cfb53afaa4d1c16e84508e

tox.ini

@@ -14,7 +14,7 @@ setenv = VIRTUAL_ENV={envdir}
 deps = -r{toxinidir}/test-requirements.txt
 
 usedevelop = True
-install_command = pip install {opts} {packages}
+install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} {opts} {packages}
 commands =
     find . -type f -name "*.pyc" -delete
     ostestr --slowest {posargs}
@@ -79,9 +79,8 @@ commands = {toxinidir}/tools/cover.sh {posargs}
 deps = -r{toxinidir}/test-requirements.txt
        sphinxcontrib-httpdomain
 commands =
-  rm -rf doc/build api-ref/build
+  rm -rf doc/build
   python setup.py build_sphinx
-  sphinx-build -W -b html api-ref/source api-ref/build/html
 
 whitelist_externals = rm
 
@@ -89,9 +88,6 @@ whitelist_externals = rm
 commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:api-ref]
-# options below are needed by CI scripts for test and publish
-# the install_command can be dropped when upstream infra supports constraints
-install_command = pip install -U --force-reinstall {opts} {packages}
 commands =
   sphinx-build -W -b html -d api-ref/build/doctrees api-ref/source api-ref/build/html