BUG-3436 Fix UNION type leaves resolution in config subsystem

BUG-3436 Fix UNION type leaves resolution in config subsystem

The descriptions for comoposite open types were not included in a reconstructed
open type, which affected resolution of subsequent composite attributes with
leaves of type union. Union leaves rely on description in order to find the
artificial JMX attribute in order to pass union value as string.

Change-Id: If6222e25840cb854e565ae476509d21ebc19ab3c
Signed-off-by: Maros Marsalek <mmarsale@cisco.com>
(cherry picked from commit 10438f09cbbeb252e58a7fb381e9dd723cc14e2e)