use super instead of direct parent call for Drive

Super allows us to call parent class without having to specify
its name, simplifying further moving of the class and possibly
more inheritance.


Change-Id: I78151e3aa7116feddbfa7f8f9d204bdafe6f95e4
Signed-off-by: Martin Polednik <mpolednik@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/32398
Reviewed-by: Francesco Romani <fromani@redhat.com>
Reviewed-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>