ConfigFile.py: improve documentation

Change-Id: I22bf0a9d38d1d14679fe65e239b45dc3c0845cfe
Signed-off-by: Mooli Tayer <mtayer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/27819
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>