DAST: auto_login does not work

Summary

While refactoring DAST's python code https://gitlab.com/gitlab-org/gitlab-ee/issues/12028, I noticed that function auto_login does not work https://gitlab.com/gitlab-org/security-products/dast/blob/master/src/zap_webdriver.py#L123.

What is the current bug behavior?

There are a couple of easy-to-fix syntax errors, e.g. self. is missing at some references.

Possible fixes

Fix the syntax and add a unit test for auto_login.