Cleanup py27 support

This repo is now testing only with Python 3, so let's make
a few cleanups:
- Remove python 2.7.3 stanza from setup.py
- Remove obsolete sections from setup.cfg
- Remove install_command from tox.ini, the default is fine
- Switch to hacking 3.0, ignore W503 and W504 (as in cinder repo)
- Use TOX_CONSTRAINTS instead of obsolete UPPER_CONSTRAINTS

Change-Id: Ia623c8af7f03c25bce7e4600693a7e834ab70000
diff --git a/tox.ini b/tox.ini
index 4c2edbc..be122b4 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,11 +9,10 @@
 [testenv]
 basepython = python3
 usedevelop = True
-install_command = pip install {opts} {packages}
 setenv =
    VIRTUAL_ENV={envdir}
    PYTHONWARNINGS=default::DeprecationWarning
-deps = -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
        -r{toxinidir}/test-requirements.txt
 commands = python setup.py test --slowest --testr-args='{posargs}'
 
@@ -25,8 +24,9 @@
 
 [flake8]
 # E123, E125 skipped as they are invalid PEP-8.
-
+# W503 line break before binary operator
+# W504 line break after binary operator
 show-source = True
-ignore = E123,E125
+ignore = E123,E125,W503,W504
 builtins = _
 exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,build