[SPARK-2259] Fix highly misleading docs on cluster / client deploy modes

The existing docs are highly misleading. For standalone mode, for example, it encourages the user to use standalone-cluster mode, which is not officially supported. The safeguards have been added in Spark submit itself to prevent bad documentation from leading users down the wrong path in the future.

This PR is prompted by countless headaches users of Spark have run into on the mailing list.

Author: Andrew Or <andrewor14@gmail.com>

Closes #1200 from andrewor14/submit-docs and squashes the following commits:

5ea2460 [Andrew Or] Rephrase cluster vs client explanation
c827f32 [Andrew Or] Clarify spark submit messages
9f7ed8f [Andrew Or] Clarify client vs cluster deploy mode + add safeguards
(cherry picked from commit f17510e371dfbeaada3c72b884d70c36503ea30a)

Signed-off-by: Patrick Wendell <pwendell@gmail.com>
[SPARK-2003] Fix python SparkContext example

Author: Matthew Farrellee <matt@redhat.com>

Closes #1246 from mattf/SPARK-2003 and squashes the following commits:

b12e7ca [Matthew Farrellee] [SPARK-2003] Fix python SparkContext example
(cherry picked from commit 0e0686d3ef88e024fcceafe36a0cdbb953f5aeae)

Signed-off-by: Patrick Wendell <pwendell@gmail.com>
Revert "[maven-release-plugin] prepare for next development iteration"

This reverts commit ea1a455a755f83f46fc8bf242410917d93d0c52c.
Revert "[maven-release-plugin] prepare release v1.0.1-rc1"

This reverts commit 7feeda3d729f9397aa15ee8750c01ef5aa601962.