Drop python 2.7 support and testing

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

python-watcherclient 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: Id66df6c12e7b533381a354937e23e33f992adbfa

.zuul.yaml

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

doc/requirements.txt

@@ -3,5 +3,4 @@
 # process, which may cause wedges in the gate later.
 
 openstackdocstheme>=1.18.1 # Apache-2.0
-sphinx!=1.6.6,!=1.6.7,>=1.6.5,<2.0.0;python_version=='2.7' # BSD
 sphinx!=1.6.6,!=1.6.7,>=1.6.5;python_version>='3.4' # BSD

releasenotes/notes/drop-py-2-7-f7078b44cf99cae1.yaml

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

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

@@ -1,6 +1,6 @@
 [tox]
 minversion = 2.0
-envlist = py36,py37,py27,pep8
+envlist = py36,py37,pep8
 skipsdist = True
 
 [testenv]