Add test for avro format MR

[piccolbo]

done, but fails of write.avro for factors, opened RA-Internal/MonsantoAvro#1

[piccolbo]

Fixed 4305695 e455306 8171bc6 but had to force a .avro extension on the input for reasons that are not totally clear but seem to prevent the input java class from producing any output. Will investigate and if necessary file upstream.

[piccolbo]

Found: https://issues.apache.org/jira/browse/AVRO-1234 will be fixed in 1.7.6 I think we can close this once we document it. Watch out since the change is considered opt in 1.7.6 so one has to set some parameter to make it work.