Draft: systemd: Better support package and upgrade.

BZ: 2081435
Tested by: QA

commit 2a4dc055c4ec628531f4bb140e157a710f874602
Author: Scott Moser <smoser@brickies.net>
Date:   Thu Sep 8 13:17:37 2016 -0400

    systemd: Better support package and upgrade.

    In systemd, package installation before the system is fully booted
    (systemctl is-system-running ==  starting) may result in the package not
    being started.  Upgrade (package_upgrade: true) can also cause failure if
    that is done during systemd boot.

    The solution here is:
     a.) move config modules that do or may do package installation to
         'final_modules'. That list is:
         - snappy
         - package-update-upgrade-install
         - fan
         - landscape
         - lxd
         - puppet
         - chef
         - salt-minion
         - mcollective
     b.) move cloud-final.service to run as 'Type=idle'

    LP: #1576692, #1621336

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>

Conflicts:
- Upstream file changes config/cloud.cfg, instead here our config file is in
rhel/cloud.cfg.
- Packages modified in upstream but not present here: byobu, snappy
- multi-user.target is already present in cloud-final.service.tmpl,
but only for ubuntu, debian and unknown variants