[DIB] disable-firewall element fails when building a CentOS or RHEL image from RHEL7

When building image using RHEL7(.3) as base (at least CentOS7 and RHEL7), the generation fails during the post-install phase of disable-firewall, inside 30-disable-firewalld.

dib-run-parts Thu Dec 22 10:10:52 EST 2016 Running /tmp/in_target.d/post-install.d/30-disable-firewalld
+ set -eu
+ set -o pipefail
+ case "${DISTRO_NAME}" in
+ which systemctl
/usr/bin/systemctl
+ systemctl disable firewalld
Operation failed: No such file or directory
++ /usr/share/diskimage-builder/lib/img-functions:run_in_target:66 : check_break after-error run_in_target bash
++ /usr/share/diskimage-builder/lib/common-functions:check_break:108 : echo ''
++ /usr/share/diskimage-builder/lib/common-functions:check_break:108 : egrep -e '(,|^)after-error(,|$)' -q
+ /usr/share/diskimage-builder/lib/img-functions:run_in_target:1 : trap_cleanup
+ /usr/share/diskimage-builder/lib/img-functions:trap_cleanup:44 : exitval=1
+ /usr/share/diskimage-builder/lib/img-functions:trap_cleanup:45 : cleanup
+ /usr/share/diskimage-builder/lib/img-functions:cleanup:50 : unmount_image
+ /usr/share/diskimage-builder/lib/img-functions:unmount_image:22 : sync
+ /usr/share/diskimage-builder/lib/img-functions:unmount_image:26 : unmount_dir /tmp/dib_build.60WTpWSk/mnt
+ /usr/share/diskimage-builder/lib/common-functions:unmount_dir:290 : local dir=/tmp/dib_build.60WTpWSk/mnt
+ /usr/share/diskimage-builder/lib/common-functions:unmount_dir:291 : local real_dir
+ /usr/share/diskimage-builder/lib/common-functions:unmount_dir:292 : local mnts
+ /usr/share/diskimage-builder/lib/common-functions:unmount_dir:294 : '[' '!' -d /tmp/dib_build.60WTpWSk/mnt ']'
++ /usr/share/diskimage-builder/lib/common-functions:unmount_dir:301 : readlink -e /tmp/dib_build.60WTpWSk/mnt
+ /usr/share/diskimage-builder/lib/common-functions:unmount_dir:301 : real_dir=/tmp/dib_build.60WTpWSk/mnt
++ /usr/share/diskimage-builder/lib/common-functions:unmount_dir:303 : grep '^/tmp/dib_build.60WTpWSk/mnt'
++ /usr/share/diskimage-builder/lib/common-functions:unmount_dir:303 : awk '{print $2}'
++ /usr/share/diskimage-builder/lib/common-functions:unmount_dir:303 : sort -r
+ /usr/share/diskimage-builder/lib/common-functions:unmount_dir:303 : mnts='/tmp/dib_build.60WTpWSk/mnt/tmp/yum
/tmp/dib_build.60WTpWSk/mnt/tmp/in_target.d
...

This may be a duplicate of https://bugs.launchpad.net/sahara/+bug/1547653, even if I was not able to reproduce it at that time. It became easier to reproduce it, but not consistently, starting from Newton (a review is already out). It's probably relate to the way host and guest variables and settings interact, and it's time to fix it (also in Newton), also because it was found by 3rd party users:
https://bugzilla.redhat.com/show_bug.cgi?id=1408251