Update tox.ini from cookiecutter changes.

- we can use usedevelop now
- use constraints
- AFAICT we don't need the hacking exception now

Change-Id: I7b6976fe6858487ca7eee323ea93b8ca4bb1aa5c

oslo.{{cookiecutter.module_name}}/tox.ini

@@ -1,32 +1,55 @@
 [tox]
-minversion = 1.6
-envlist = py34,py26,py27,pypy,pep8
-# NOTE(dhellmann): We cannot set skipdist=True
-# for oslo libraries because of the namespace package.
-#skipsdist = True
+minversion = 1.8
+envlist = py34-constraints,py27-constraints,pypy-constraints,pep8-constraints
+skipsdist = True
 
 [testenv]
-# NOTE(dhellmann): We cannot set usedevelop=True
-# for oslo libraries because of the namespace package.
-#usedevelop = True
-install_command = pip install -U {opts} {packages}
+usedevelop = True
+install_command =
+                  constraints: {[testenv:common-constraints]install_command}
+                  pip install -U {opts} {packages}
 setenv =
    VIRTUAL_ENV={envdir}
-deps = -r{toxinidir}/requirements.txt
-       -r{toxinidir}/test-requirements.txt
-commands = python setup.py testr --slowest --testr-args='{posargs}'
+deps = -r{toxinidir}/test-requirements.txt
+commands = python setup.py test --slowest --testr-args='{posargs}'
+
+[testenv:common-constraints]
+install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} {opts} {packages}
 
 [testenv:pep8]
-commands = flake8
+commands = flake8 {posargs}
+
+[testenv:pep8-constraints]
+install_command = {[testenv:common-constraints]install_command}
+commands = flake8 {posargs}
 
 [testenv:venv]
 commands = {posargs}
 
+[testenv:venv-constraints]
+install_command = {[testenv:common-constraints]install_command}
+commands = {posargs}
+
+[testenv:cover]
+commands = python setup.py test --coverage --testr-args='{posargs}'
+
+[testenv:cover-constraints]
+install_command = {[testenv:common-constraints]install_command}
+commands = python setup.py test --coverage --testr-args='{posargs}'
+
 [testenv:docs]
 commands = python setup.py build_sphinx
 
-[testenv:cover]
-commands = python setup.py testr --coverage --testr-args='{posargs}'
+[testenv:docs-constraints]
+install_command = {[testenv:common-constraints]install_command}
+commands = python setup.py build_sphinx
+
+[testenv:debug]
+commands = oslo_debug_helper {posargs}
+
+[testenv:debug-constraints]
+install_command = {[testenv:common-constraints]install_command}
+commands = oslo_debug_helper {posargs}
 
 [flake8]
 # E123, E125 skipped as they are invalid PEP-8.
@@ -35,6 +58,3 @@ show-source = True
 ignore = E123,E125
 builtins = _
 exclude=.venv,.git,.tox,dist,doc,*openstack/common*,*lib/python*,*egg,build
-
-[hacking]
-import_exceptions =