Cleanup py27 support

This repo is now testing only with Python 3, so let's make
a few cleanups:
- Remove obsolete sections from setup.cfg
- Remove install_command from tox.ini, the default is fine
- move basepython into testenv
- use TOX_CONSTRAINTS_FILE instead of obsolete UPPER_CONSTRAINTS_FILE
- update pbr to current versions

Change-Id: Iae3f34e63d5a7d84bcc74716e490bd3b02bcab52

setup.cfg

@@ -9,6 +9,3 @@ classifier =
     Intended Audience :: Developers
     License :: OSI Approved :: Apache Software License
     Operating System :: POSIX :: Linux
-
-[wheel]
-universal = 1

test-requirements.txt

@@ -1,2 +1,2 @@
-pbr>=0.6,!=0.7,<1.0
+pbr!=2.1.0,>=2.0.0 # Apache-2.0
 bashate >= 0.2

tox.ini

@@ -4,15 +4,14 @@ minversion = 1.6
 skipsdist = True
 
 [testenv]
-install_command = pip install -U {opts} {packages}
+basepython = python3
 setenv = VIRTUAL_ENV={envdir}
 deps =
-  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+  -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/test-requirements.txt
 passenv = GENERATE_GRENADE_PLUGIN_LIST
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [testenv:bashate]
@@ -20,10 +19,9 @@ commands =
   bash -c "ls *.sh prep-* stop-* upgrade-* from-*/upgrade-* functions | xargs bashate -v {posargs}"
 
 [testenv:docs]
-basepython = python3
 whitelist_externals = bash
 deps =
-  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+  -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/doc/requirements.txt
 setenv =
   TOP_DIR={toxinidir}