Add SELinux secontext handling when packing the rootfs .

[rsiddoji]

Hi team ,
Current krikstone branch code when handling rootfs folder for creating ostree based rootfs folder its not considering selinux .
Following is the patch that will try to pass selinux option to tar utility .
If the rootfs is already labeled with selinux it will preserve the labels else it will be NOP (https://www.gnu.org/software/tar/manual/tar.html)
Can you please help to get this review and help us on how we can merge this change .

Attaching the single line changes

0001-RFC-meta-updater-adding-selinux-support-for-in-packi.patch

Regards,
Ravi.,

[ricardosalveti]

Please propose the same change as a pull request against https://github.com/uptane/meta-updater instead (master first then as a backport once merged). Thanks!