add recommends on systemd-cryptsetup, Closes: #1078792
Fixes https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1078792. Explanation of fix at https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1078792#15. tl;dr: systemd-cryptsetup is required for unlocking the disk but isn't a Recommends of the dracut package, so it ends up not being installed on the end user's system and thus dracut is unable to unlock the disk.