hydra-module: Avoid creating /root/r in compressLogs cronjob.

We really don't need to touch a file in the current working directory to find files that are older than one month. Since findutils 4.3.3 there is a `-newerXY` option which allows to specify timestamps directly (as with `date --date`).

But even when using a reference file, it really causes confusion if people look into `/root` and try to debug where that misterious `r` file is coming from.