DRILL-5325: Unit tests for the managed sort
Uses the sub-operator test framework (DRILL-5318), including the test
row set abstraction (DRILL-5323) to enable unit testing of the
“managed” external sort. This PR allows early review of the code, but
cannot be pulled until the dependencies (mentioned above) are pulled.
Refactors the external sort code into small chunks that can be unit
tested, then “wraps” that code in tests for all interesting data types,
record batch sizes, and so on.
Refactors some of the operator definitions to more easily allow
programmatic setup in the unit tests.
Fixes a number of bugs discovered by the unit tests. The biggest
changes were in the new code: the code that computes spilling and
merging based on memory levels.
Otherwise, although GitHub will show many files change, most of the
changes are simply moving blocks of code around to create smaller units
that can be tested independently.
Includes a refactoring of the code that does spilling, along with a
complete set of low-level unit tests.
Excludes long-running sort tests.
Defines a test category for long-running tests.
First attempt to provide a way to run such tests from Maven.
closes #808
