Add dummy functional test tox target

OpenStack-CI is executing a functional test against stable/mitaka
but there are no tests to run.

This patch adds a dummy tox target as a placeholder. If tests are
added in the future then they can replace this content.

Change-Id: Ifd915e7cda3961942f827fbb4d713964b79e1399

tox.ini

@@ -40,6 +40,7 @@ commands =
         --exclude-dir doc \
         {toxinidir} | xargs flake8 --verbose"
 
+
 [flake8]
 # Ignores the following rules due to how ansible modules work in general
 #     F403 'from ansible.module_utils.basic import *' used;
@@ -70,5 +71,11 @@ commands =
     {[testenv:pep8]commands}
     {[testenv:bashate]commands}
 
+
+[testenv:functional]
+commands =
+    echo '============ No Functional tests to run just yet. ============'
+
+
 [testenv:releasenotes]
 commands = sphinx-build -a -E -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html