Add doc/requirements

We need to specify doc requirements in doc/requirements.txt
to avoid problems with the pip resolver [1] for the release team [2][3].
Removing specific doc requirements from test-requirements.txt.

The problem here is that this repos haven't doc/requirements.txt file
and by default in this case zuul will use the test-requirements.txt file
to pull requirements [4].

This requirements file contains extra requirements like flake8 that
collided with those allowed in our job environment and so the new pip
resolver fails to install these requirements and the job exits in error.
It also update horizon version in requirements.txt to match the horizon
version in  lower-constriants.txt to fix requirements-check job.

This project meet the conditions leading to the bug.

[1] http://lists.openstack.org/pipermail/release-job-failures/2021-January/001500.html
[2] http://lists.openstack.org/pipermail/openstack-discuss/2021-January/019611.html
[3] http://lists.openstack.org/pipermail/openstack-discuss/2021-January/019612.html
[4] https://opendev.org/zuul/zuul-jobs/src/branch/master/roles/ensure-sphinx/tasks/main.yaml#L36

Change-Id: I425e9b4cfcf86e67c6288796e3da95b07769c6dc

doc/requirements.txt

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

requirements.txt

@@ -15,4 +15,4 @@ castellan>=0.18.0 # Apache-2.0
 oslo.log>=3.36.0 # Apache-2.0
 semantic-version>=2.3.1 # BSD
 
-horizon>=18.3.0 # Apache-2.0
+horizon>=18.3.1 # Apache-2.0

test-requirements.txt

@@ -9,12 +9,6 @@ coverage!=4.4,>=4.0 # Apache-2.0
 oslo.config>=5.2.0 # Apache-2.0
 selenium>=2.50.1 # Apache-2.0
 
-
-# Docs Requirements
-openstackdocstheme>=2.2.1 # Apache-2.0
-sphinx>=2.0.0,!=2.1.0 # BSD
-reno>=3.1.0 # Apache-2.0
-
 # Horizon requirements
 django-compressor>=2.0 # MIT
 

tox.ini

@@ -43,12 +43,15 @@ commands = nodeenv -p
            npm install
            npm run lint
 
-[testenv:releasenotes]
-commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
-
 [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
+
 [flake8]
 # H202: assertRaises Exception too broad
 ignore = H202,W504