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

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

ceilometer 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

Depends-On: https://review.opendev.org/#/c/693631/

Change-Id: Ie8523712ea2ebe828fe01a649b6add90e813608b

.zuul.yaml

@@ -19,8 +19,7 @@
 - project:
     templates:
       - openstack-cover-jobs
-      - openstack-python-jobs
-      - openstack-python3-train-jobs
+      - openstack-python3-ussuri-jobs
       - publish-openstack-docs-pti
       - periodic-stable-jobs
       - release-notes-jobs-python3

doc/requirements.txt

@@ -1,4 +1,3 @@
-sphinx!=1.6.6,!=1.6.7,>=1.6.2,<2.0.0;python_version=='2.7'  # BSD
 sphinx!=1.6.6,!=1.6.7,>=1.6.2;python_version>='3.6'  # BSD
 sphinxcontrib-httpdomain>=1.3.0 # BSD
 sphinxcontrib-blockdiag>=1.5.4 # BSD

releasenotes/notes/drop-py-2-7-87352d5763131c13.yaml

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

requirements.txt

@@ -4,7 +4,6 @@
 
 cachetools>=2.1.0 # MIT License
 cotyledon>=1.3.0 #Apache-2.0
-futures>=3.0;python_version=='2.7' or python_version=='2.6' # BSD
 futurist>=1.8.0 # Apache-2.0
 jsonpath-rw-ext>=1.1.3 # Apache-2.0
 lxml>=3.4.1 # BSD

setup.cfg

@@ -14,8 +14,6 @@ classifier =
     License :: OSI Approved :: Apache Software License
     Operating System :: POSIX :: Linux
     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

@@ -1,9 +1,10 @@
 [tox]
 minversion = 2.0
 skipsdist = True
-envlist = py{27,36,37},pep8
+envlist = py{36,37},pep8
 
 [testenv]
+basepython = python3
 deps = -r{toxinidir}/test-requirements.txt
        -r{toxinidir}/requirements.txt
        -c{env:UPPER_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/branch/master/upper-constraints.txt}
@@ -18,7 +19,6 @@ commands =
 whitelist_externals = bash
 
 [testenv:cover]
-basepython = python3
 setenv =
     PYTHON=coverage run --source ceilometer --parallel-mode
 commands =
@@ -28,7 +28,6 @@ commands =
     coverage xml -o cover/coverage.xml
 
 [testenv:pep8]
-basepython = python3
 deps = hacking<0.13,>=0.12
        doc8
 commands =
@@ -38,22 +37,18 @@ commands =
     bash -c "find ceilometer -type f -regex '.*\.pot?' -print0|xargs -0 -n 1 msgfmt --check-format -o /dev/null"
 
 [testenv:releasenotes]
-basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:genconfig]
-basepython = python3
 commands = oslo-config-generator --config-file=etc/ceilometer/ceilometer-config-generator.conf
 
 [testenv:docs]
-basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 commands = sphinx-build -b html doc/source doc/build/html
 setenv = PYTHONHASHSEED=0
 
 [testenv:pdf-docs]
-basepython = python3
 deps = {[testenv:docs]deps}
 whitelist_externals =
   make
@@ -62,7 +57,6 @@ commands =
   make -C doc/build/pdf
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 setenv = PYTHONHASHSEED=0
 
@@ -81,7 +75,6 @@ import_exceptions =
 local-check-factory = ceilometer.hacking.checks.factory
 
 [testenv:lower-constraints]
-basepython = python3
 deps =
   -c{toxinidir}/lower-constraints.txt
   -r{toxinidir}/test-requirements.txt