[SQL] Decrease partitions when testing

Author: Michael Armbrust <michael@databricks.com>

Closes #2164 from marmbrus/shufflePartitions and squashes the following commits:

0da1e8c [Michael Armbrust] test hax
ef2d985 [Michael Armbrust] more test hacks.
2dabae3 [Michael Armbrust] more test fixes
0bdbf21 [Michael Armbrust] Make parquet tests less order dependent
b42eeab [Michael Armbrust] increase test parallelism
80453d5 [Michael Armbrust] Decrease partitions when testing