Dtest library does not know to work with interfaces

Instrumentator.injectOnCall does not work with interfaces. It can work just with classes.
The call like this does not work and causing that rule is not bound
instrumentor.injectOnCall(SomeInterface.class, "someMethod", "traceln(\"someMethod on interface called\")");

The reason is that the rule is constructed with word "CLASS" and there is no way how to say that the injection should be provided on INTERFACE.

Attempt for fix is here
https://github.com/bytemanproject/byteman/pull/23