SPARK-3093 : masterLock in Worker is no longer need

there's no need to use masterLock in Worker now since all communications are within Akka actor

Author: CrazyJvm <crazyjvm@gmail.com>

Closes #2008 from CrazyJvm/no-need-master-lock and squashes the following commits:

dd39e20 [CrazyJvm] fix format
58e7fa5 [CrazyJvm] there's no need to use masterLock now since all communications are within Akka actor
[SPARK-2862] histogram method fails on some choices of bucketCount

Author: Chandan Kumar <chandan.kumar@imaginea.com>

Closes #1787 from nrchandan/spark-2862 and squashes the following commits:

a76bbf6 [Chandan Kumar] [SPARK-2862] Fix for a broken test case and add new test cases
4211eea [Chandan Kumar] [SPARK-2862] Add Scala bug id
13854f1 [Chandan Kumar] [SPARK-2862] Use shorthand range notation to avoid Scala bug
SPARK-3096: Include parquet hive serde by default in build

A small change - we should just add this dependency. It doesn't have any recursive deps and it's needed for reading have parquet tables.

Author: Patrick Wendell <pwendell@gmail.com>

Closes #2009 from pwendell/parquet and squashes the following commits:

e411f9f [Patrick Wendell] SPARk-309: Include parquet hive serde by default in build
[SPARK-3084] [SQL] Collect broadcasted tables in parallel in joins

BroadcastHashJoin has a broadcastFuture variable that tries to collect
the broadcasted table in a separate thread, but this doesn't help
because it's a lazy val that only gets initialized when you attempt to
build the RDD. Thus queries that broadcast multiple tables would collect
and broadcast them sequentially. I changed this to a val to let it start
collecting right when the operator is created.

Author: Matei Zaharia <matei@databricks.com>

Closes #1990 from mateiz/spark-3084 and squashes the following commits:

f468766 [Matei Zaharia] [SPARK-3084] Collect broadcasted tables in parallel in joins