Move some test requirements to tox.ini

Simplify requirements management.

Also increase minversion of tox to support inline comments [1]

https://tox.readthedocs.io/en/latest/changelog.html#v3-9-0-2019-04-17

Change-Id: I5d5e526cedbdd70ea8ee8eaa8fe847baa72fc275

test-requirements.txt

@@ -2,8 +2,6 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 
-hacking>=3.1.0,<4.0.0 # Apache-2.0
-
 coverage!=4.4,>=4.0 # Apache-2.0
 # used by libvirt driver
 libvirt-python>=6.0.0 # LGPLv2+
@@ -15,5 +13,3 @@ stestr>=1.0.0 # Apache-2.0
 testscenarios>=0.4 # Apache-2.0/BSD
 testtools>=2.2.0 # MIT
 munch>=2.1.0 # MIT
-flake8-import-order>=0.17.1 # LGPLv3
-pycodestyle>=2.0.0,<2.7.0 # MIT

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-minversion = 3.2.1
+minversion = 3.9.0
 envlist = py3,pep8
 skipsdist = True
 ignore_basepython_conflict=true
@@ -18,6 +18,10 @@ commands = stestr run {posargs}
            stestr slowest
 
 [testenv:pep8]
+deps =
+    hacking>=3.1.0,<4.0.0 # Apache-2.0
+    flake8-import-order>=0.17.1 # LGPLv3
+    pycodestyle>=2.0.0,<2.7.0 # MIT
 commands = flake8 {posargs}
 
 [testenv:venv]