DIB fails to build bionic using ubuntu-minimal (rsyslog)

[Michael Johnson]

When using the ubuntu-minimal element to build a bionic image, DIB fails the build with the following error:

2019-01-09 15:06:12.928 | > Setting up rsyslog (8.32.0-1ubuntu4) ...
2019-01-09 15:06:12.928 | >
2019-01-09 15:06:12.928 | > Creating config file /etc/rsyslog.d/50-default.conf with new version
2019-01-09 15:06:12.928 | > Adding user `syslog' to group `adm' ...
2019-01-09 15:06:12.928 | > Adding user syslog to group adm
2019-01-09 15:06:12.928 | > Done.
2019-01-09 15:06:12.928 | > Unsafe symlinks encountered in /var/spool/rsyslog, refusing.
2019-01-09 15:06:12.928 | > Unsafe symlinks encountered in /var/log, refusing.
2019-01-09 15:06:12.928 | > dpkg: error processing package rsyslog (--configure):
2019-01-09 15:06:12.928 | > installed rsyslog package post-installation script subprocess returned error exit status 1

This only happens on bionic hosts running diskimage-builder. The image creates successfully on xenial hosts.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/629744

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/629744
Committed: https://git.openstack.org/cgit/openstack/diskimage-builder/commit/?id=cfba9ea79d903574afe58bbe3964c050676ee8da
Submitter: Zuul
Branch: master

commit cfba9ea79d903574afe58bbe3964c050676ee8da
Author: Michael Johnson <email address hidden>
Date: Wed Jan 9 18:27:59 2019 -0800

    Make sure $TMP_BUILD_DIR/mnt is owned by root

    The path $TMP_BUILD_DIR/mnt becomes the / inside the chroot during
    the chroot phases of diskimage-builder. Previously this path was being
    created using the account running diskimage-builder. This account may
    not be valid inside the chroot. This causes path validation, when running
    on a Ubuntu bionic host, to fail.
    This patch chown's the $TMP_BUILD_DIR/mnt to root.root to make sure
    that / is owned by a valid account inside the chroot.

    Change-Id: Ifedc136baa67c7952942aed2c8cb1041902fef91
    Closes-Bug: 1811113