[SPARK-2283][SQL] Reset test environment before running PruningSuite

JIRA issue: [SPARK-2283](https://issues.apache.org/jira/browse/SPARK-2283)

If `PruningSuite` is run right after `HiveCompatibilitySuite`, the first test case fails because `srcpart` table is cached in-memory by `HiveCompatibilitySuite`, but column pruning is not implemented for `InMemoryColumnarTableScan` operator yet.

Author: Cheng Lian <lian.cs.zju@gmail.com>

Closes #1221 from liancheng/spark-2283 and squashes the following commits:

dc0b663 [Cheng Lian] SPARK-2283: reset test environment before running PruningSuite

(cherry picked from commit 7f196b009d26d4aed403b3c694f8b603601718e3)
Signed-off-by: Michael Armbrust <michael@databricks.com>
[SPARK-1749] Job cancellation when SchedulerBackend does not implement killTask

This is a fixed up version of #686 (cc @markhamstra @pwendell).  The last commit (the only one I authored) reflects the changes I made from Mark's original patch.

Author: Mark Hamstra <markhamstra@gmail.com>
Author: Kay Ousterhout <kayousterhout@gmail.com>

Closes #1219 from kayousterhout/mark-SPARK-1749 and squashes the following commits:

42dfa7e [Kay Ousterhout] Got rid of terrible double-negative name
80b3205 [Kay Ousterhout] Don't notify listeners of job failure if it wasn't successfully cancelled.
d156d33 [Mark Hamstra] Do nothing in no-kill submitTasks
9312baa [Mark Hamstra] code review update
cc353c8 [Mark Hamstra] scalastyle
e61f7f8 [Mark Hamstra] Catch UnsupportedOperationException when DAGScheduler tries to cancel a job on a SchedulerBackend that does not implement killTask
(cherry picked from commit b88a59a66845b8935b22f06fc96d16841ed20c94)

Signed-off-by: Patrick Wendell <pwendell@gmail.com>
[SPARK-2172] PySpark cannot import mllib modules in YARN-client mode

Include pyspark/mllib python sources as resources in the mllib.jar.
This way they will be included in the final assembly

Author: Szul, Piotr <Piotr.Szul@csiro.au>

Closes #1223 from piotrszul/branch-1.0 and squashes the following commits:

69d5174 [Szul, Piotr] Removed unsed resource directory src/main/resource from mllib pom
f8c52a0 [Szul, Piotr] [SPARK-2172] PySpark cannot import mllib modules in YARN-client mode Include pyspark/mllib python sources as resources in the jar