Normalize the Gerrit URL in a cross-Django manner.
Review Request #10229 — Created Oct. 13, 2018 and discarded — Latest diff uploaded
URLFieldon Django 1.6 will add a trailing/to a URL without an
explicit path, whereas newer versions will not. Since Gerrit goes out of
its way to check the resulting URLs from the field, we need consistency
across the versions. To be future-proof, we now strip the trailing/
when cleaning the form.
The relevant unit tests pass on Django 1.6 and 1.11.