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

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

heat-tempest-plugin is ready with python 3 and ok to drop the
python 2.7 support.

Stable zuul jobs are modified to run with py3 as heat-tempest-plugin
cannot run py2 jobs on master gate.

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: Ida6919a70dc8711166a79eac574b0714382e8d00

.zuul.yaml

@@ -1,6 +1,6 @@
 - job:
     name: heat-functional-convg-queens
-    parent: heat-functional-convg-mysql-lbaasv2
+    parent: heat-functional-convg-mysql-lbaasv2-py3
     nodeset: legacy-ubuntu-xenial
     override-checkout: stable/queens
     vars:
@@ -13,10 +13,11 @@
     nodeset: legacy-ubuntu-xenial
     vars:
       branch_override: stable/queens
+      use_python3: 1
 
 - job:
     name: heat-functional-convg-rocky
-    parent: heat-functional-convg-mysql-lbaasv2
+    parent: heat-functional-convg-mysql-lbaasv2-py3
     override-checkout: stable/rocky
     nodeset: legacy-ubuntu-xenial
     vars:
@@ -29,10 +30,11 @@
     nodeset: legacy-ubuntu-xenial
     vars:
       branch_override: stable/rocky
+      use_python3: 1
 
 - job:
     name: heat-functional-convg-stein
-    parent: heat-functional-convg-mysql-lbaasv2
+    parent: heat-functional-convg-mysql-lbaasv2-py3
     override-checkout: stable/stein
     nodeset: legacy-ubuntu-xenial
     vars:
@@ -45,10 +47,11 @@
     nodeset: legacy-ubuntu-xenial
     vars:
       branch_override: stable/stein
+      use_python3: 1
 
 - job:
     name: heat-functional-convg-train
-    parent: heat-functional-convg-mysql-lbaasv2
+    parent: heat-functional-convg-mysql-lbaasv2-py3
     override-checkout: stable/train
     nodeset: legacy-ubuntu-xenial
     vars:
@@ -61,6 +64,7 @@
     nodeset: legacy-ubuntu-xenial
     vars:
       branch_override: stable/train
+      use_python3: 1
 
 - project:
     templates:

setup.cfg

@@ -13,10 +13,10 @@ 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 :: 3.5
+    Programming Language :: Python :: 3.6
+    Programming Language :: Python :: 3.7
 
 keywords =
     setup

tox.ini

@@ -1,9 +1,11 @@
 [tox]
-envlist = py27,py35,pep8
-minversion = 0.1
+envlist = py37,pep8
+minversion = 3.1.1
 skipsdist = True
+ignore_basepython_conflict = True
 
 [testenv]
+basepython = python3
 userdevelop = True
 setenv = VIRTUAL_ENV={envdir}
 deps = -r{toxinidir}/requirements.txt
@@ -12,7 +14,6 @@ commands = bash -c 'if [ ! -d ./.testrepository ] ; then testr init ; fi'
            testr run {posargs}
 
 [testenv:pep8]
-basepython = python3
 setenv =
     PYTHONPATH = .
 commands =
@@ -26,7 +27,6 @@ commands =
     check-uuid --fix --package heat_tempest_plugin
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [flake8]