fix(dracut-initramfs-restore.sh): hide unpack errors

[aafeijoo-suse]

With the current "try and fail" approach, the system log contains errors until
the correct initrd compression is reached.

E.g. extra error log produced by a zstd compressed initrd, until the right option is reached:

Aug 17 09:42:18 localhost.localdomain dracut-initramfs-restore[6670]: gzip: stdin: not in gzip format
Aug 17 09:42:18 localhost.localdomain dracut-initramfs-restore[6671]: cpio: premature end of archive
Aug 17 09:42:18 localhost.localdomain dracut-initramfs-restore[6669]: ERROR: src/skipcpio/skipcpio.c:191:main(): fwrite
Aug 17 09:42:18 localhost.localdomain dracut-initramfs-restore[6675]: bzcat: (stdin) is not a bzip2 file.
Aug 17 09:42:18 localhost.localdomain dracut-initramfs-restore[6674]: ERROR: src/skipcpio/skipcpio.c:191:main(): fwrite
Aug 17 09:42:18 localhost.localdomain dracut-initramfs-restore[6676]: cpio: premature end of archive
Aug 17 09:42:18 localhost.localdomain dracut-initramfs-restore[6680]: xzcat: (stdin): File format not recognized
Aug 17 09:42:18 localhost.localdomain dracut-initramfs-restore[6681]: cpio: premature end of archive
Aug 17 09:42:18 localhost.localdomain dracut-initramfs-restore[6679]: ERROR: src/skipcpio/skipcpio.c:191:main(): fwrite
Aug 17 09:42:18 localhost.localdomain dracut-initramfs-restore[6686]: /usr/lib/dracut/dracut-initramfs-restore: line 57: lz4: command not found
Aug 17 09:42:18 localhost.localdomain dracut-initramfs-restore[6685]: ERROR: src/skipcpio/skipcpio.c:191:main(): fwrite
Aug 17 09:42:18 localhost.localdomain dracut-initramfs-restore[6687]: cpio: premature end of archive
Aug 17 09:42:18 localhost.localdomain dracut-initramfs-restore[6689]: /usr/lib/dracut/dracut-initramfs-restore: line 58: lzop: command not found
Aug 17 09:42:18 localhost.localdomain dracut-initramfs-restore[6688]: ERROR: src/skipcpio/skipcpio.c:191:main(): fwrite
Aug 17 09:42:18 localhost.localdomain dracut-initramfs-restore[6690]: cpio: premature end of archive

Checklist

• I have tested it locally
• I have reviewed and updated any documentation if relevant
• I am providing new code and test(s) for it

[LaszloGombos]

LGTM

[johannbg]

LGTM