yum check-update in redhat/centos lxc container creation fails if updates are available

[Jeff Albert]

During LXC container creation, a bash script is built to prep the container environment with platform-specific actions.

https://github.com/openstack/openstack-ansible-lxc_container_create/blob/stable/rocky/templates/container-setup.sh.j2

One of those actions for RedHat/CentOS is a `yum check-update`, followed immediately by a full `yum -y update` to actually apply updates that are available.

https://github.com/openstack/openstack-ansible-lxc_container_create/blob/stable/rocky/vars/redhat-7.yml#L44

However, the output of check-update is never used, and it by design returns a non-zero return code if updates are available to be installed, which means the script fails because it implements `set -ev`, which fails the whole script if any subcommand fails.

The `yum check-update` command is superfluous in this action set, and I think should be removed.

[Jeff Albert (jralbert)]

Argh, moments too late I discovered this change, which does the removal I'm proposing, in the stein branch:

https://github.com/openstack/openstack-ansible-lxc_container_create/commit/b15b97fa0ab73579e4939ae767a2810196b33df2#diff-0dc9e326c64f4a15341a43e16b94ee60

Can/should this be backported to Rocky?