Add an integration tests which generates a key

Configuring an online account generates a key, we would like this
code-path tested too.  So add some functionality to the AccountManager
to not use the pre-generated keys.

Because this slows down interactively running the tests by hand add an
ignored marker which only runs if --ignored is used.  This name was
chosen because this matches the naming used by rust/cargo #[ignored].
The difference however is that --ignored on cargo *only* runs ignored
tests while here it runs *all* tests.

To ensure the ignored/slow tests are run on CI we add it as an
argument to the tox configuration, which is used by the CI to run the
tests.

python/tests/test_account.py

@@ -417,6 +417,12 @@ class TestOfflineChat:
 
 
 class TestOnlineAccount:
+    @pytest.mark.ignored
+    def test_configure_generate_key(self, acfactory):
+        # A slow test which will generate a new key.
+        ac = acfactory.get_one_online_account(pre_generated_key=False)
+        ac.check_is_configured()
+
     def get_chat(self, ac1, ac2, both_created=False):
         c2 = ac1.create_contact(email=ac2.get_config("addr"))
         chat = ac1.create_chat_by_contact(c2)