pep8: Fix pep8 in vdsm-tool

Added PEP8_WHITELIST to avoid such things in the future.

Change-Id: I00773932002cdeac939afedad90f1291010fedda
Signed-off-by: Dima Kuznetsov <dkuznets@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/27656
Reviewed-by: Dan Kenigsberg <danken@redhat.com>