Emulate GitHub source tarfile naming

[mulkieran]

No description provided.

[bgurney-rh]

This almost worked, but not quite; mock failed to find the directory after the tar file was extracted.

I just tested this, and it works:

    source_tarfile_path = make_source_tarball(
        "stratisd", f"stratisd-v{release_version}", output_path
    )

I'll add this to a PR that updates mockbuild_test/stratisd.spec. (I didn't discover this until I updated the "mock --rebuild" command to add "--no-cleanup-after", so I could run "ls" in the /var/lib/mock directory of the chroot config (e.g.: ls /var/lib/mock/fedora-rawhide-x86_64/root/builddir/build/BUILD). By default, the buildroot is cleaned up afterward, even after a failure.