Add support for virt-sandbox-service to add additional mount points.

Add similar support to virt-sandbox-service that is in virt-sandbox
to add guest-bind, host-bind and host-image mount points on the command
line.  Openshift needs feature.
Allow user to specify additional rpm packages to be run within the container.

Example would be I want to run cron with sendmail.

virt-sandbox-service create -u crond.service -P sendmail mycron
Only create the tmpfs file systems in the systemd containers.

Openshift wants /tmp, /dev/shm and /var/tmp mounted from the users homedir.
Removing doc directive which was breaking build on F19