Add doc/requirements

Specify doc requirements needs to be moved out from
test-requirements.txt to in doc/requirements.txt
to avoid problems with the pip resolver as announced by
the release team [1].

[1] http://lists.openstack.org/pipermail/openstack-discuss/2021-January/019611.html

Change-Id: Iac9a3421c23370f19f57d6aa84c2862ccfce2a94

doc/requirements.txt

@@ -0,0 +1,3 @@
+sphinx>=2.0.0,!=2.1.0 # BSD
+openstackdocstheme>=2.2.1 # Apache-2.0
+reno>=3.1.0 # Apache-2.0

test-requirements.txt

@@ -9,10 +9,7 @@ ddt>=1.0.1 # MIT
 docker>=2.4.2 # Apache-2.0
 stestr>=1.0.0 # Apache-2.0
 oslo.serialization!=2.19.1,>=2.18.0 # Apache-2.0
-openstackdocstheme>=2.2.1 # Apache-2.0
 oslotest>=3.2.0 # Apache-2.0
 python-subunit>=1.0.0 # Apache-2.0/BSD
-reno>=3.1.0 # Apache-2.0
-sphinx>=2.0.0,!=2.1.0 # BSD
 testscenarios>=0.4 # Apache-2.0/BSD
 testtools>=2.2.0 # MIT

tox.ini

@@ -46,6 +46,8 @@ commands =
     coverage report
 
 [testenv:docs]
+deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+       -r{toxinidir}/doc/requirements.txt
 commands =
   sphinx-build -a -W -E -b html doc/source doc/build/html
 
@@ -72,6 +74,7 @@ local-check-factory = neutron_lib.hacking.checks.factory
 commands = {toxinidir}/tools/generate_config_file_samples.sh
 
 [testenv:releasenotes]
+deps = {[testenv:docs]deps}
 commands = sphinx-build -a -W -E -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:lower-constraints]