fix handling of 404 errors in firewall rule checks

What critical bug this MR is fixing?

This fixes the on-demand creation of firewall rules. That's needed for bootstrapping docker-machine for local development work, which will contribute towards cost saving improvements.

For example https://gitlab.com/gitlab-com/Finance-Division/finance/-/issues/6738.

How does this change help reduce cost of usage? What scale of cost reduction is it?

Not directly.

In what scenarios is this change usable with GitLab Runner's docker+machine executor?

I can run the fork locally if needed. It'll suck for anyone else who wants to test out docker-machine locally though.