Changes

Fix validation in Endpoint constructor

There is an additional level of validation on the endpoint address
inside the constructor in Endpoint.java.
This validation was wrong as it didn't allow local URLs (i.e.,
localhost).
This led to endpoint addresses being silently converted to null during
code generation.

Signed-off-by: Moritz Marseu <moritz.marseu@festo.com>
Change-Id: I4b52dea1b61bd1322787e50ad89af47a93e1cc12