py3: Switch to using Python 3 for rocky or later

Switch package install to Python 3 for OpenStack Rocky or later.

Change-Id: Ia309566c96d024c08dfddb1559ab903d4d5fa4dc
Depends-On: I17a93524fb7ec134b4a3a61cd0e86977daf49c4e

src/lib/charm/openstack/designate.py

@@ -641,7 +641,9 @@ class DesignateCharmRocky(DesignateCharmQueens):
     packages = ['designate-agent', 'designate-api', 'designate-central',
                 'designate-common', 'designate-mdns',
                 'designate-worker', 'designate-sink',
-                'designate-producer', 'bind9utils', 'python-apt']
+                'designate-producer', 'bind9utils',
+                'python3-designate',
+                'python-apt']
 
     services = ['designate-mdns', 'designate-producer',
                 'designate-agent', 'designate-worker',
@@ -655,3 +657,12 @@ class DesignateCharmRocky(DesignateCharmQueens):
         '/etc/designate/pools.yaml': [''],
         RC_FILE: [''],
     }
+
+    purge_packages = [
+        'python-designate',
+        'python-memcache',
+        'designate-zone-manager',
+        'designate-pool-manager',
+    ]
+
+    python_version = 3

src/tox.ini

@@ -35,7 +35,7 @@ commands =
 # Run a specific test as an Amulet smoke test (expected to always pass)
 basepython = python2.7
 commands =
-    bundletester -vl DEBUG -r json -o func-results.json gate-basic-bionic-queens --no-destroy
+    bundletester -vl DEBUG -r json -o func-results.json gate-basic-bionic-rocky --no-destroy
 
 [testenv:func27-dfs]
 # Run all deploy-from-source tests which are +x (may not always pass!)