Use functional tox environment

Create new functional tox environment so that we can use it instead of
func environment to allow creation of cross-project
openstack-tox-functional job.

Depends-On: Ibebf9d0eeccabaefa2777a43592a72d19d064b6b
Needed-By: Ifa4c20cff72820a0016bef8dcdd36647ae7359d3
Change-Id: Ied08d83177b9d52b6eb8e4987f444230ac4ebfdb

tox.ini

@@ -6,6 +6,13 @@ skipsdist = True
 commands = {posargs}
 
 [testenv:func]
+# Replaced in CI with "functional" environment but kept here as a
+# backwards-compatibility shim for transition
+changedir={toxinidir}/tests
+envdir = {toxworkdir}/venv
+commands = {[testenv:functional]commands}
+
+[testenv:functional]
 changedir={toxinidir}/tests
 envdir = {toxworkdir}/venv
 commands = ./run_tests.sh {posargs}