This update for mksusecd fixes the following issues:

- Embed gpg signature of checksum metadata into image. (bsc#1139561)
- Set the default to unsigned images.
- Add --enable-repos option.
- Support aarch64 media.
- No longer assume repo-md repositories don't include the installer. (bsc#1093145)
- Adjust isozipl according to the changes of isoinfo. (bsc#1097814)
- Don't miss zstd compression module. (bsc#1100236)
- Keep some meta data for media checking even if the filesystem does not use iso9660. (bsc#1000947)
- adjust to isoinfo and syslinux changes (bsc#1097814)

This update was imported from the SUSE:SLE-15:Update update project.