Bug 762: Fix sal-rest-connector unit tests

The cnsn-to-json/simple-data-types/xml/data.xml test file used by
CnSnToJsonBasicDataTypesTest actually contains some invalid union type data.
The tests currently pass because union type input data isn't currently
validated. Patch https://git.opendaylight.org/gerrit/#/c/7367/
in yangtools adds validation so the unit tests must be fixed before
that patch is merged.

In addition, the yangtools patch changes some static fields in
TypeDefinitionAwareCodec to private which breaks compilation of
CnSnToXmlTest. This patch modifies CnSnToXmlTest to not use the static
fields.

Change-Id: I020ffacd4a6c96265a191fa74f982de807e336a4
Signed-off-by: tpantelis <tpanteli@brocade.com>
Merge "Bug 762: Fix sal-rest-connector unit tests"