Make non-verbose mkarchiso more quiet

Running mkarchiso without -v still produces some output from the tools it runs:

mkfs.fat 4.2 (2021-01-31)
Unrecognised xattr prefix system.posix_acl_default
Unrecognised xattr prefix system.posix_acl_access
Unrecognised xattr prefix system.posix_acl_default
Unrecognised xattr prefix system.posix_acl_access
Unrecognised xattr prefix system.posix_acl_default
xorriso 1.5.4 : RockRidge filesystem manipulator, libburnia project.

xorriso : NOTE : Environment variable SOURCE_DATE_EPOCH encountered with value 1629566829
833M    /tmp/archiso-out/archlinux-2021.08.21-x86_64.iso

• mkfs.fat does not have a -q/--quiet option. https://github.com/dosfstools/dosfstools/issues/103.
• xorriso still produces messages even with -quiet. This is despite xorrisofs(1) saying "Suppress most messages of the program run, except those which indicate problems or errors".
• The output from mksquashfs is expected since squashfs does not support ACLs.
• mkfs.erofs does not have a -q/--quiet option and it outputs to stderr instead of stdout.

Additionally, in netboot build mode:

663M    /tmp/archiso-out/arch/x86_64
20K     /tmp/archiso-out/arch/boot/licenses/memtest86+
4.0K    /tmp/archiso-out/arch/boot/licenses/amd-ucode
4.0K    /tmp/archiso-out/arch/boot/licenses/intel-ucode
28K     /tmp/archiso-out/arch/boot/licenses
77M     /tmp/archiso-out/arch/boot/x86_64
82M     /tmp/archiso-out/arch/boot
745M    /tmp/archiso-out/arch

• du output is needlessly verbose.