Rename parent volume in blockSD.getAllVolumes.

Renaming variable names for better readability.

Change-Id: I62f1385e4af90a923c5d97a71571bea8780aa339
Signed-off-by: Eduardo <ewarszaw@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/8608
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>