- Added pure immutable test yamls to integ test framework. Added SparkBulkInsertNode as part of it.
- Added delete_partition support to integ test framework using spark-datasource.
- Added a single yaml to test all non core write operations (insert overwrite, insert overwrite table and delete partitions)
- Added tests for 4 concurrent spark datasource writers (multi-writer tests).
- Fixed readme w/ sample commands for multi-writer.
