Drop lower-constraints.txt and its testing

As discussed in TC PTG[1] and TC resolution[2], we are
dropping the lower-constraints.txt file and its testing.
We will keep lower bounds in the requirements.txt file but
with a note that these are not tested lower bounds and we
try our best to keep them updated.

[1] https://etherpad.opendev.org/p/tc-zed-ptg#L326
[2] https://governance.openstack.org/tc/resolutions/20220414-drop-lower-constraints.html#proposal

This also makes the following two changes to fix the broken CI.

- Switch the python3 job template to unversioned one because
  the heat-cfntools project follows an independent release model.
  This effectively removes py36 tests.

- Use upper-constraints.txt to build documentation, to avoid pulling
  the latest Sphinx which includes a breaking change.

Change-Id: I3c41ed7cd54e8c8d3fad05ea7ac86fc35b9fa4d1

.zuul.yaml

@@ -1,6 +1,5 @@
 - project:
     templates:
       - check-requirements
-      - openstack-lower-constraints-jobs
-      - openstack-python3-wallaby-jobs
+      - openstack-python3-jobs
       - publish-openstack-docs-pti

doc/source/conf.py

@@ -65,7 +65,7 @@ copyright = 'OpenStack Foundation'
 #
 # This is also used if you do content translation via gettext catalogs.
 # Usually you set "language" from the command line for these cases.
-language = None
+language = 'en'
 
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.

lower-constraints.txt

@@ -1,6 +0,0 @@
-boto==2.32.1
-pbr==2.0.0
-psutil==1.1.1
-six==1.9.0
-stestr==2.0.0
-testtools==0.9.34

requirements.txt

@@ -1,3 +1,7 @@
+# Requirements lower bounds listed here are our best effort to keep them up to
+# date but we do not test them so no guarantee of having them all correct. If
+# you find any incorrect lower bounds, let us know or propose a fix.
+
 pbr!=2.1.0,>=2.0.0
 boto>=2.32.1
 psutil>=1.1.1

tox.ini

@@ -5,7 +5,8 @@ ignore_basepython_conflict = true
 [testenv]
 basepython = python3
 setenv = VIRTUAL_ENV={envdir}
-deps =-c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+deps =
+    -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
     -r{toxinidir}/requirements.txt
     -r{toxinidir}/test-requirements.txt
 commands = stestr run --slowest {posargs}
@@ -32,11 +33,7 @@ show-source = true
 exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,tools
 
 [testenv:docs]
-deps = -r{toxinidir}/doc/requirements.txt
-commands = sphinx-build -W -b html doc/source doc/build/html
-
-[testenv:lower-constraints]
 deps =
-  -c{toxinidir}/lower-constraints.txt
-  -r{toxinidir}/requirements.txt
-  -r{toxinidir}/test-requirements.txt
+    -c{env:UPPER_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