Add doc/requirements

We need to specify doc requirements in doc/requirements.txt
to avoid problems with the pip resolver for the release team.
Removed specific doc requirements from test-requirements.txt

Change-Id: Ia88848fd9c4ce35d396bc186ae3894a1d5865db9

doc/requirements.txt

@@ -0,0 +1,4 @@
+reno>=3.1.0 # Apache-2.0
+sphinx>=2.0.0,!=2.1.0 # BSD
+openstackdocstheme>=2.2.1 # Apache-2.0
+

test-requirements.txt

@@ -7,10 +7,6 @@ hacking>=3.2.0,<3.3.0 # Apache-2.0
 coverage!=4.4,>=4.0 # Apache-2.0
 flake8-import-order==0.12 # LGPLv3
 python-subunit>=1.0.0 # Apache-2.0/BSD
-sphinx>=2.0.0,!=2.1.0 # BSD
 oslotest>=3.2.0 # Apache-2.0
 stestr>=1.0.0 # Apache-2.0
 testtools>=2.2.0 # MIT
-openstackdocstheme>=2.2.1 # Apache-2.0
-# releasenotes
-reno>=3.1.0 # Apache-2.0

tox.ini

@@ -39,9 +39,12 @@ commands =
     coverage xml -o cover/coverage.xml
 
 [testenv:docs]
+deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+       -r{toxinidir}/doc/requirements.txt
 commands = sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:releasenotes]
+deps = {[testenv:docs]deps}
 commands =
   sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html