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: I323b079ec538ebc2184724325fad00bbe2092e9b

src/tests/basic_deployment.py

@@ -68,7 +68,8 @@ class DesignateBasicDeployment(amulet_deployment.OpenStackAmuletDeployment):
             self.get_percona_service_entry(),
             {'name': 'rabbitmq-server'},
             {'name': 'keystone'},
-            {'name': 'memcached', 'location': 'cs:memcached'},
+            {'name': 'memcached',
+             'location': 'cs:~memcached-team/memcached'},
             {'name': 'designate-bind'},
             {'name': 'neutron-api'}
         ]

src/tox.ini

@@ -4,13 +4,17 @@
 [tox]
 envlist = pep8
 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}
          PYTHONHASHSEED=0
          AMULET_SETUP_TIMEOUT=5400
 whitelist_externals = juju
-passenv = HOME TERM AMULET_* CS_*
+passenv = HOME TERM AMULET_* CS_* OS_*
 deps = -r{toxinidir}/test-requirements.txt
 install_command =
   pip install {opts} {packages}

tox.ini

@@ -4,7 +4,10 @@
 [tox]
 skipsdist = True
 envlist = pep8,py37
-skip_missing_interpreters = 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}
@@ -53,7 +56,7 @@ deps = -r{toxinidir}/test-requirements.txt
 commands = stestr run {posargs}
 
 [testenv:pep8]
-basepython = python3.5
+basepython = python3
 deps = -r{toxinidir}/test-requirements.txt
 commands = flake8 {posargs} src unit_tests