Convert tests to Python 3

Fix #938

system/t12_api/systemd_handover.py

@@ -1,5 +1,7 @@
 import requests_unixsocket
-import urllib
+import urllib.error
+import urllib.parse
+import urllib.request
 import os
 import os.path
 
@@ -42,5 +44,5 @@ class SystemdAPIHandoverTest(BaseTest):
             print("Skipping test as we failed to setup a listener.")
             return
         session = requests_unixsocket.Session()
-        r = session.get('http+unix://%s/api/version' % urllib.quote(self.socket_path, safe=''))
+        r = session.get('http+unix://%s/api/version' % urllib.parse.quote(self.socket_path, safe=''))
         self.check_equal(r.json(), {'Version': os.environ['APTLY_VERSION']})