DRILL-1185: Unit test for delimited text failing in classpath storage plugin.
DRILL-1458: New unit test framework.

Review comments, cleanup, additional tests

Matching columns, throw useful error messages if there are missing or extra columns.

Few more features in unit test framework, providing several baseline records in the builder pattern, allow checking empty result. Added a new unit test to ensure that nulls were validated properly in both the ordered and unordered cases.
DRILL-1737: Fix decimal handling in unit test framework.
DRILL-1775: Fix BINARY ENUM in Parquet converter.
DRILL-1749: Support nested maps in the flatten operator.
DRILL-1753: Flatten 2 level repeated map
DRILL-1787: Fix memory leak in kvgen function.
Fix for flatten receiving a non-repeated type during fast schema step.
DRILL-1748: Fix SplitUpComplexExpressions rule when using Item operator