ConfigFile.py: include default section wrapping comments.

Since ConfigFile.py represents common operations on config files
it should also include the default comments vdsm inserts.
Only version has no default to allow different callares
have different configuration version.

Change-Id: I54b6b10d64d4a2d299e8fc783880c92c07dedd7b
Signed-off-by: Mooli Tayer <mtayer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/27820
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>