unified_persistence: Fix whitelist value types

The upgrade script didn't convert the types to what the vdsm schema
expects for the data in the whitelist.

This patch addresses that by having a dictionary that has a value
handling method for each of the elements in the whitelist.

Change-Id: Ib1859a57b44f1ba1f2e32ff83e26e9e9fbf8228c
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/27058
Reviewed-by: Dan Kenigsberg <danken@redhat.com>