testing-farm: properly handle sidetag repository
    
    This is a follow up for #163.
    
    As it turned out, in case of a sidetag repo, the repo.url
    is the url to the repo file, not directly the repo base url.
    
    So this PR parses out the repo url from the repo file.
    
    Tested via:
    
    ```
    ❯ ansible -c local -m debug -e repo_url='https://centos.softwarefactory-project.io/logs/14/14/ad79fadaffb361d47f36a0c7597d449702a832b8/check/mock-build/bb0a33c/sidetag.repo' -a "msg={{ lookup('ansible.builtin.url', repo_url) | regex_search('baseurl=([^,]+)', '\\1') }}" localhost
    localhost | SUCCESS => {
        "msg": [
            "https://kojihub.stream.centos.org/kojifiles/repos/c9s-build-side-1485-stack-gate/latest/x86_64/"
        ]
    }
    ```
    
    Signed-off-by: Miroslav Vadkerti <mvadkert@redhat.com>