yum-minimal : install selinux policy packages
yum-minimal : install selinux policy packages

Install selinux policy packages as part of the base-installs.  selinux
is part of the base-system and the kernel boots by default in selinux
mode.

Without both of these, we can get in a situation where later scripts
(particuarly, some of the infra scripts) might install systemd-policy
without a base policy (targeted), leading to a messed up situation
where systemd will halt during boot due to missing policy files.

Change-Id: I6bf156304d1134fb328fba9b12dc364701b13696

openstack/diskimage-builder,takahashinobuyuki/diskimage-builder,switch-ch/diskimage-builder,CSC-IT-Center-for-Science/diskimage-builder,CSC-IT-Center-for-Science/diskimage-builder,openstack/diskimage-builder,zioproto/diskimage-builder,switch-ch/diskimage-builder,zioproto/diskimage-builder,takahashinobuyuki/diskimage-builder