[SPARK-3235][SQL] Ensure in-memory tables don't always broadcast.

Author: Michael Armbrust <michael@databricks.com>

Closes #2147 from marmbrus/inMemDefaultSize and squashes the following commits:

5390360 [Michael Armbrust] Merge remote-tracking branch 'origin/master' into inMemDefaultSize
14204d3 [Michael Armbrust] Set the context before creating SparkLogicalPlans.
8da4414 [Michael Armbrust] Make sure we throw errors when leaf nodes fail to provide statistcs
18ce029 [Michael Armbrust] Ensure in-memory tables don't always broadcast.
HOTFIX: Don't build with YARN support for Mapr3
Add line continuation for script to work w/ py2.7.5

Error was -

$ SPARK_HOME=$PWD/dist ./dev/create-release/generate-changelist.py
  File "./dev/create-release/generate-changelist.py", line 128
    if day < SPARK_REPO_CHANGE_DATE1 or
                                      ^
SyntaxError: invalid syntax

Author: Matthew Farrellee <matt@redhat.com>

Closes #2139 from mattf/master-fix-generate-changelist.py-0 and squashes the following commits:

6b3a900 [Matthew Farrellee] Add line continuation for script to work w/ py2.7.5