Fix remote access for non-default usernames

Fixed Ska archive remote access to work correctly when the username is
not the local user (the "username" argument does not work - it has to be
set in the servername: "<username>@<hostname>").

@mbaski - just discovered this commit which was orphaned in the remote-fetch-faster-stats branch.  You put this commit after I merged the original PR and I didn't realize (or maybe forgot).  I just rebased to get a clean new PR with just this update.