Add Endpoint and Method Name to COPROC_EXEC Spans

If we assume parentBased=on, then it's enough to add this information on the client side.
However, we may want to also add this on the server side for stochastic tracing.

We could call these:

db.hbase.endpoint.name
db.hbase.endpoint.method

or 

db.hbase.coprocessor.name
db.hbase.coprocessor.method