Fixed wrong exception types

Fixed wrong exception types

- After implementation of exception mapper we can throw on error
  events RestconfDocumentedException that will be automatically
  mapped to response errors container.
- This patch changes IAE or NPE during serialization/deserialition
  of instance identifier to right RDE types - HTTP method invoked
  on non-existing/malformed IID will lead to returned errors
  container (compliancy against spec.) and not status code 500
  without any description.

Change-Id: I0982e89b90d4a254656b2b9dcdab87fcbb4a8103
Signed-off-by: Jaroslav Tóth <jtoth@frinx.io>
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>