Add integration tests to verify logging

[gokulavasan]

One of the common pain points in debugging CDAP MapReduce (which includes Hydrator pipelines) has been missing logs - which means we need to ask the user to go to MR container logs using UI or cmdline and this is not ideal. Sometimes this is fixed in Release X and in Release X+1 there is retrogression and we don't catch it. In order to avoid this completely, we need an integration test case to make sure we collect MR logs - this might be accomplished by hitting the logs endpoint or we might need to add a new LogClient. The test should also make sure that the MR program throws exceptions and those logs are also captured (in addition to the successful completion path). Also add System.out/err.println in Mapper/Reducer logic to make sure we are capturing those statements too.