Add disco-stein bundle to gate tests

The bundle disco-stein was in the dev bundles because
a bug with the Python 3.7 syntax prevented the success of
the deployment of HA clusters. This bug is fixed, we can
reintegrate disco-stein in the gate bundles.

Other small additions:
- removing sitepackages in tox.ini to avoid test env pollution
- skip_missing_interpreters in tox.ini set to False to avoid false
positives by skipping missing interpreters.

LP Related-Bug: #1823718

Change-Id: If15188c82c21c24d404b9b7620fc042b8be70143

tests/basic_deployment.py

@@ -77,7 +77,8 @@ class CeilometerBasicDeployment(OpenStackAmuletDeployment):
         if self._get_openstack_release() >= self.xenial_pike:
             other_services.extend([
                 {'name': 'gnocchi'},
-                {'name': 'memcached', 'location': 'cs:memcached'},
+                {'name': 'memcached',
+                 'location': 'cs:~memcached-team/memcached'},
                 {'name': 'ceph-mon', 'units': 3},
                 {'name': 'ceph-osd', 'units': 3,
                  'storage': {'osd-devices': 'cinder,10G'}}])

tox.ini

@@ -4,6 +4,10 @@
 [tox]
 envlist = pep8,py37
 skipsdist = True
+# NOTE(beisner): Avoid build/test env pollution by not enabling sitepackages.
+sitepackages = False
+# NOTE(beisner): Avoid false positives by not skipping missing interpreters.
+skip_missing_interpreters = False
 
 [testenv]
 setenv = VIRTUAL_ENV={envdir}