[ussuri][goal] Drop python 2.7 support

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

specs repo either has py27 job or requirement or tox env.

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

Change-Id: Ia6d4378abf5ee92f371236a081b82157a9c88682

.zuul.yaml

@@ -3,7 +3,7 @@
       - openstack-specs-jobs
     check:
       jobs:
-        - openstack-tox-py27
+        - openstack-tox-py37
     gate:
       jobs:
-        - openstack-tox-py27
+        - openstack-tox-py37

doc/source/conf.py

@@ -30,7 +30,6 @@ import warnings
 extensions = ['sphinx.ext.autodoc',
               'sphinx.ext.todo',
               'sphinx.ext.viewcode',
-              'oslosphinx',
               'yasfb',
              ]
 

requirements.txt

@@ -1,5 +1,4 @@
-oslosphinx
-pbr>=1.6
-sphinx>=1.1.2,<1.2
+pbr!=2.1.0  # Apache-2.0
+sphinx!=1.6.6,!=1.6.7,!=2.1.0,>=1.6.2;python_version>='3.4'  # BSD
 testtools>=0.9.34
-yasfb>=0.5.1
+yasfb

tox.ini

@@ -1,9 +1,11 @@
 [tox]
-minversion = 2.0
-envlist = py27,docs
+minversion = 3.1.1
+envlist = pep8,docs
 skipsdist = True
+ignore_basepython_conflict = True
 
 [testenv]
+basepython = python3
 usedevelop = True
 install_command = pip install -U {opts} {packages}
 setenv =
@@ -17,11 +19,9 @@ commands =
     stestr run --slowest {posargs}
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [testenv:docs]
-basepython = python3
 commands =
     find . -type f -name "*.pyc" -delete
     python setup.py build_sphinx