Test case: Abort half way through a transaction

[fpj]

Add a test case that aborts part way into writing events from a file. Currently, the test enabled with duringTxnFlag aborts after all events have been written but before commit:

https://github.com/fpj/eo-ingestion/blob/master/src/test/java/io/pravega/eoi/PravegaSynchronizedWriterTest.java#L79

This is a good test. However, another interesting test would be aborting after just a few of the events in a transaction have been written. Specifically, I mean aborting part way in the loop that begins here:

https://github.com/fpj/eo-ingestion/blob/master/src/main/java/io/pravega/eoi/PravegaSynchronizedWriter.java#L232