[SPARK-11275][SQL] Incorrect results when using rollup/cube

Fixes bug with grouping sets (including cube/rollup) where aggregates that included grouping expressions would return the wrong (null) result.

Also simplifies the analyzer rule a bit and leaves column pruning to the optimizer.

Added multiple unit tests to DataFrameAggregateSuite and verified it passes hive compatibility suite:
```
build/sbt -Phive -Dspark.hive.whitelist='groupby.*_grouping.*' 'test-only org.apache.spark.sql.hive.execution.HiveCompatibilitySuite'
```

This is an alternative to pr https://github.com/apache/spark/pull/9419 but I think its better as it simplifies the analyzer rule instead of adding another special case to it.

Author: Andrew Ray <ray.andrew@gmail.com>

Closes #9815 from aray/groupingset-agg-fix.