Coin shouldn't keep files that failed to transfer

Apparently this integration failed horribly with a timeout on MacOS_13.

The errors in the log look unrepairable, even sccache -s at the end times out instead of producing valid statistics.

Apparently in this testrun, the Coin agent failed to transfer the testresults tarball to the Coin server, because in the downloads section the file is zero bytes long.

This corrupt file is not a valid tarball and shouldn't be there, the transfer-error should have been caught on the Coin server, and the corrupt file should have been deleted.