Pass all CS_ vars to tox env to pickup timeout

Change-Id: I9b63f5edf7aaa3e2d106579d30ae9f90930b7f95

src/tox.ini

@@ -10,7 +10,7 @@ setenv = VIRTUAL_ENV={envdir}
          PYTHONHASHSEED=0
          AMULET_SETUP_TIMEOUT=5400
 whitelist_externals = juju
-passenv = HOME TERM AMULET_*
+passenv = HOME TERM AMULET_* CS_*
 deps = -r{toxinidir}/test-requirements.txt
 install_command =
   pip install {opts} {packages}