Fix broken test in spec/models/project_spec.rb

A test was broken if running on a non-standard port. Made checking for (non-)standard port more robust. Changed gitlab_on_non_standard_port to gitlab_on_standard_port (less negative).

Too explain the reasoning behind changing gitlab_on_non_standard_port: The previous check just looked at whether the port was 443 or 80. This one checks that it is 443 if https otherwise 80 for http.