Removing update of 'node.startup' setting in 'addIscsiPortal'

I removed not working code in 'addIscsiPortal' method. It supposed
to update 'node.startup' setting to 'manual', but used 'discoverydb'
operational mode instead of 'node' what caused to exception.

Change-Id: Ib34952047367db196733e942416a232d12a4e491
Bug-Url: https://bugzilla.redhat.com/851050
Signed-off-by: Sergey Gotliv <sgotliv@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/17212
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-by: Ayal Baron <abaron@redhat.com>