vdscli: rename constants and make them private

the various d_* constants found in the vdscli
module should not be exported and their naming
should reflect they are private.

Change-Id: I525505f6bdf77db9595539c3f67b3399447c3242
Signed-off-by: Francesco Romani <fromani@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/35272
Reviewed-by: Piotr Kliczewski <piotr.kliczewski@gmail.com>
Reviewed-by: Yeela Kaplan <ykaplan@redhat.com>
Reviewed-by: mooli tayer <mtayer@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>