Fix Rspec error when using non-default port

Prevent test failures when GitLab is configured to use a port other than
80.
Use actual GitLab URL for test assertion

Assert the full GitLab root URL, including the port, instead of using a
regexp to tolerate whatever port is returned.
Merge pull request #8053 from mr-vinn/fix-rspec-url

Fix Rspec error when using non-default port