BUG 2412 - restconf @POST createConfigurationData method migration

BUG 2412 - restconf @POST createConfigurationData method migration

* migration to new faster Infrastructure API and Codecs for method
@POST createConfigurationData(String,NormalizedNodeContext,UriInfo)
on @Path {/config/identifier}

New faster Infrastructure API works with NormizedNodeContext and
we are replacing createConfigurationData method from RestconfService
to use NormalizedNodeContext.

* add additional functionality to find a correct child DataSchemaNode
for @POST input payload in XmlNormalizedNodeBodyReader

* add fix or comment tests - problem with RestconfDocumentedExceptionMapper
      - it has to be fixed in future commit in this chain

Change-Id: I8348002aaa817bc4816a0d132f5811fa84eda389
Signed-off-by: Vaclav Demcak <vdemcak@cisco.com>