[SPARK-5658][SQL] Finalize DDL and write support APIs

https://issues.apache.org/jira/browse/SPARK-5658

Author: Yin Huai <yhuai@databricks.com>

This patch had conflicts when merged, resolved by
Committer: Michael Armbrust <michael@databricks.com>

Closes #4446 from yhuai/writeSupportFollowup and squashes the following commits:

f3a96f7 [Yin Huai] davies's comments.
225ff71 [Yin Huai] Use Scala TestHiveContext to initialize the Python HiveContext in Python tests.
2306f93 [Yin Huai] Style.
2091fcd [Yin Huai] Merge remote-tracking branch 'upstream/master' into writeSupportFollowup
537e28f [Yin Huai] Correctly clean up temp data.
ae4649e [Yin Huai] Fix Python test.
609129c [Yin Huai] Doc format.
92b6659 [Yin Huai] Python doc and other minor updates.
cbc717f [Yin Huai] Rename dataSourceName to source.
d1c12d3 [Yin Huai] No need to delete the duplicate rule since it has been removed in master.
22cfa70 [Yin Huai] Merge remote-tracking branch 'upstream/master' into writeSupportFollowup
d91ecb8 [Yin Huai] Fix test.
4c76d78 [Yin Huai] Simplify APIs.
3abc215 [Yin Huai] Merge remote-tracking branch 'upstream/master' into writeSupportFollowup
0832ce4 [Yin Huai] Fix test.
98e7cdb [Yin Huai] Python style.
2bf44ef [Yin Huai] Python APIs.
c204967 [Yin Huai] Format
a10223d [Yin Huai] Merge remote-tracking branch 'upstream/master' into writeSupportFollowup
9ff97d8 [Yin Huai] Add SaveMode to saveAsTable.
9b6e570 [Yin Huai] Update doc.
c2be775 [Yin Huai] Merge remote-tracking branch 'upstream/master' into writeSupportFollowup
99950a2 [Yin Huai] Use Java enum for SaveMode.
4679665 [Yin Huai] Remove duplicate rule.
77d89dc [Yin Huai] Update doc.
e04d908 [Yin Huai] Move import and add (Scala-specific) to scala APIs.
cf5703d [Yin Huai] Add checkAnswer to Java tests.
7db95ff [Yin Huai] Merge remote-tracking branch 'upstream/master' into writeSupportFollowup
6dfd386 [Yin Huai] Add java test.
f2f33ef [Yin Huai] Fix test.
e702386 [Yin Huai] Apache header.
b1e9b1b [Yin Huai] Format.
ed4e1b4 [Yin Huai] Merge remote-tracking branch 'upstream/master' into writeSupportFollowup
af9e9b3 [Yin Huai] DDL and write support API followup.
2a6213a [Yin Huai] Update API names.
e6a0b77 [Yin Huai] Update test.
43bae01 [Yin Huai] Remove createTable from HiveContext.
5ffc372 [Yin Huai] Add more load APIs to SQLContext.
5390743 [Yin Huai] Add more save APIs to DataFrame.