Dtest class instrumentor functionality is not thread safe

I've hit trouble of multi-thread usage of dtest library. If used InstrumentedClass and check instances or number of calls and there is a higher load of traces to be written and checked later it can happen that some of the traces is not written to map as it's not concurrent ready. Similar thing could happen in helper on the server side.

See
https://github.com/bytemanproject/byteman/blob/7863aa2c8e28c1568276422259ff490f2957b3ee/contrib/dtest/src/org/jboss/byteman/contrib/dtest/InstrumentedClass.java#L44