BUG 2282 - JSON top level element without module name

Json top level element now doesn't have to contain module name prefix.

If namespace of some child element was changed and only one child with
specified name exist in schema then its namespace is used by default.

If more then one potential child in various namespaces exists then
exception is raised. Exception is also raised if no such element as
specified in JSON input exists in YANG schema.

Change-Id: I8a38fde4f2e9b79562f6bf7c79acafd51c7bff32
Signed-off-by: Jozef Gloncak <jgloncak@cisco.com>
Merge "BUG 2282 - JSON top level element without module name" into stable/helium