tests: do not fail with multipart emails

tests/utilities.py

@@ -162,10 +162,14 @@ class EmailsMocking(object):
             def sendmail(self, msg_from, rcpts, msg):
                 msg = email.parser.Parser().parsestr(msg)
                 subject = email.header.decode_header(msg['Subject'])[0][0]
+                if msg.is_multipart():
+                    payload = msg.get_payload()[0].get_payload(decode=True)
+                else:
+                    payload = msg.get_payload(decode=True)
                 self.emails[subject] = {
                         'from': msg_from,
                         'to': email.header.decode_header(msg['To'])[0][0],
-                        'payload': msg.get_payload(decode=True),
+                        'payload': payload,
                         }
                 self.emails[subject]['email_rcpt'] = rcpts