Update tox.ini files from release-tools gold copy

All OpenStack Charms now contain identical tox.ini files,
not to be modified or made unique within each charm repo.

This is to ensure consistency across charm repos in tox
target naming, approach and purpose, also giving the
charm dev and test experience additional consistency.

Change-Id: I180bc53ca131f37d569be1bfcd4e24df1eca3e93

tox.ini

@@ -1,3 +1,6 @@
+# Classic charm: ./tox.ini
+# This file is managed centrally by release-tools and should not be modified
+# within individual charm repos.
 [tox]
 envlist = pep8,py27
 skipsdist = True
@@ -6,10 +9,11 @@ skipsdist = True
 setenv = VIRTUAL_ENV={envdir}
          PYTHONHASHSEED=0
          AMULET_SETUP_TIMEOUT=2700
-passenv = HOME TERM AMULET_*
 install_command =
   pip install --allow-unverified python-apt {opts} {packages}
 commands = ostestr {posargs}
+whitelist_externals = juju
+passenv = HOME TERM AMULET_*
 
 [testenv:py27]
 basepython = python2.7
@@ -72,4 +76,4 @@ commands =
 
 [flake8]
 ignore = E402,E226
-exclude = hooks/charmhelpers
+exclude = */charmhelpers