Fixes undercloud install failure with setting hostname

Fixes undercloud install failure with setting hostname

There is a new bug when deploying master/rocky where the OS of the
undercloud/overcloud is now upgraded to CentOS 7.6. When the undercloud
install runs it fails to configure the hostname using hostnamectl. This
is because systemd-hostnamed is not running and fails to start. Simply
reloading dbus seems to fix the issue. In the dbus logs there are odd
error messages like:

dbus-daemon[3230]: Unknown username "root" in message bus configuration
file

Disabling selinux seems to fix this. This patch also moves to use
podman instead of docker for container management and invokes a script
in Ansible which updates NIC templates as new variables are added
upstream. Furthermore, with the new patches for routed networks in OOO,
it is now required that the MTU is set in network-data, as well as
adding the External network to the Compute role. Now the External
network is removed by default from the Compute role.

Change-Id: Ie8b86f6f28d69bda11b1f7a430df882970ac3cb9
Signed-off-by: Tim Rozet <trozet@redhat.com>