Drop python 2.7 support and testing

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

vitrage-tempest-plugin 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://review.opendev.org/#/c/691178/

Change-Id: Ic6d010d7e14933d9fd2bc39f157af54147f4401d

releasenotes/notes/drop-py-2-7-1be17025c498d4bd.yaml

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

requirements.txt

@@ -25,5 +25,4 @@ oslo.utils>=3.36.0 # Apache-2.0
 testtools>=2.2.0 # MIT
 oslotest>=3.2.0 # Apache-2.0
 tempest>=17.1.0 # Apache-2.0
-networkx<2.3,>=2.0;python_version<'3.0'  # BSD
 networkx>=2.3;python_version>='3.4'  # BSD

setup.cfg

@@ -13,8 +13,6 @@ 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

@@ -17,12 +17,15 @@ deps = -r{toxinidir}/test-requirements.txt
 commands = stestr run {posargs}
 
 [testenv:pep8]
+basepython = python3
 commands = flake8 {posargs}
 
 [testenv:venv]
+basepython = python3
 commands = {posargs}
 
 [testenv:cover]
+basepython = python3
 setenv =
     VIRTUAL_ENV={envdir}
     PYTHON=coverage run --source virtage_tempest_plugin --parallel-mode
@@ -33,13 +36,16 @@ commands =
     coverage xml -o cover/coverage.xml
 
 [testenv:docs]
+basepython = python3
 commands = python setup.py build_sphinx
 
 [testenv:releasenotes]
+basepython = python3
 commands =
   sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:debug]
+basepython = python3
 commands = oslo_debug_helper {posargs}
 
 [flake8]