[ussuri][goal] Drop python 2.7 support and testing

OpenStack is dropping the py2.7 support in ussuri cycle.

freezer is ready with python 3 and ok to drop the
python 2.7 support.

Complete discussion & schedule can be found in
- http://lists.openstack.org/pipermail/openstack-discuss/2019-October/010142.html
- https://etherpad.openstack.org/p/drop-python2-support

Ussuri Communtiy-wide goal:
https://governance.openstack.org/tc/goals/selected/ussuri/drop-py27.html

Change-Id: I14ab74f3e82e83ef5c5a49831f68335965e7e101

.zuul.yaml

@@ -2,7 +2,6 @@
     templates:
       - check-requirements
       - openstack-lower-constraints-jobs
-      - openstack-python-jobs
       - openstack-python3-ussuri-jobs
       - publish-openstack-docs-pti
       - release-notes-jobs-python3

doc/requirements.txt

@@ -1,7 +1,6 @@
 # The order of packages is significant, because pip processes them in the order
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
-sphinx>=1.6.5,!=1.6.6,!=1.6.7,<2.0.0;python_version=='2.7' # BSD
 sphinx>=1.6.5,!=1.6.6,!=1.6.7,!=2.1.0;python_version>='3.4' # BSD
 sphinxcontrib-apidoc>=0.2.0  # BSD
 openstackdocstheme>=1.20.0 # Apache-2.0

releasenotes/notes/drop-py-2-7-a76d53b7a12bcff2.yaml

@@ -0,0 +1,6 @@
+---
+upgrade:
+  - |
+    Python 2.7 support has been dropped. Last release of freezer
+    to support py2.7 is OpenStack Train. The minimum version of Python now
+    supported by freezer is Python 3.6.

setup.cfg

@@ -8,8 +8,6 @@ home-page = https://docs.openstack.org/freezer/latest/
 license = Apache-2
 classifier =
     Programming Language :: Python
-    Programming Language :: Python :: 2
-    Programming Language :: Python :: 2.7
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7

tox.ini

@@ -1,8 +1,9 @@
 [tox]
-envlist = py27,py37,pep8,pylint,docs
+envlist = py37,pep8,pylint,docs
 skipsdist = True
 
 [testenv]
+basepython = python3
 usedevelop = True
 deps =
     -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
@@ -46,12 +47,8 @@ python_files = test_*.py
 norecursedirs  = .tox .venv
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
-[testenv:py27]
-basepython = python2.7
-
 [testenv:py37]
 basepython = python3.7
 
@@ -59,7 +56,6 @@ basepython = python3.7
 basepython = python3.6
 
 [testenv:docs]
-basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 whitelist_externals = rm
 commands =
@@ -68,13 +64,11 @@ commands =
 
 
 [testenv:pep8]
-basepython = python3
 commands =
     flake8 freezer
     doc8 {posargs}
 
 [testenv:pylint]
-basepython = python3
 commands = pylint --rcfile .pylintrc freezer
 
 [flake8]
@@ -88,7 +82,6 @@ ignore = D000,D001
 ignore-path = .venv,.git,.tox,.tmp,*freezer/locale*,*lib/python*,freezer.egg*,doc/build,releasenotes/*,doc/source/contributor/api
 
 [testenv:releasenotes]
-basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 whitelist_externals = rm
 commands =
@@ -96,7 +89,6 @@ commands =
   sphinx-build -a -E -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:lower-constraints]
-basepython = python3
 deps =
   -c{toxinidir}/lower-constraints.txt
   -r{toxinidir}/test-requirements.txt