trivial: Cleanup tox.ini

Update the minversion parameter to use the python -m pip to install
python packages:

https://tox.readthedocs.io/en/latest/changelog.html#id185

Also Inherit the jobs requirements to simplify maintainance.

Change-Id: Ib6e94fa9f822830242a99f6690349569626f1931

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-minversion = 3.1
+minversion = 3.2.0
 envlist = py37,pep8
 ignore_basepython_conflict = true
 
@@ -7,14 +7,11 @@ ignore_basepython_conflict = true
 basepython = python3
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
- -r{toxinidir}/test-requirements.txt
+  -r{toxinidir}/test-requirements.txt
- -r{toxinidir}/requirements.txt
 commands = stestr run --slowest {posargs}
 
 [testenv:pep8]
-deps =
+deps = {[testenv]deps}
-  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
-  -r{toxinidir}/test-requirements.txt
 commands =
   flake8
   # Run security linter
@@ -52,9 +49,7 @@ import_exceptions =
 
 [testenv:releasenotes]
 whitelist_externals = rm
-deps =
+deps = {[testenv:docs]deps}
-  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
-  -r{toxinidir}/doc/requirements.txt
 commands =
   rm -rf releasenotes/build
   sphinx-build -a -E -W -d releasenotes/build/doctrees --keep-going -b html releasenotes/source releasenotes/build/html