[GSS](7.1.z) Revise Java 8 default methods support

As it seems Weld does not support Java 8 default methods completely. We need to be sure that for any bean that needs subclassing (interceptors/decorators) and which implements an interface with a default method:

the default method which has no interceptor associated is invoked correctly
the default method which has an interceptor associated is invoked correctly
verify that the self-invocation of a default method (similarly as tested in org.jboss.weld.tests.interceptors.self.SelfInvocationTest) does not trigger interception
Or at least know which parts are problematic and need our attention.