Bug#818592: control: split and improve dependency handling for disk detection

[Hendrik Brueckner <brueckner@linux.vnet.ibm.com>]

Package: s390-zfcp
Version: 1.0.1
Severity: important
Tags: d-i

To improve and provide a "guided" flow, split the harddrive
detection dependency for s390-dasd and s390-zfcp as follows:

- s390-dasd provides harddrive-detection-dasd
- s390-zfcp provides harddrive-detection-zfcp

The disk-detect package depends on
  -> harddrive-detection-dasd
  -> harddrive-detection-zfcp

and continues to provide the harddrive-detection.  With this split,
installation on mixed DASD and SCSI disks are possible.  Also move
the module before the disk-detect module in the Debian installer
menu.

See also related Debian Bug #818586 for the disk-detect package.

Patch for the control file will follow.

Thanks and kind regards,
  Hendrik