rework check for xorriso version and be more verbose about its usage

rework check for xorriso version and be more verbose about its usage

Don't run any [U]EFI related actions if we don't have a recent version
of xorriso, and be verbose about what we do.

While at it check for xorriso version>= 1.1.6-1, so it works with
1.1.6-2~bpo60+1 from grml-infrastructure repos too.