Tweaks to Mesos docs

- Mention Apache downloads first
- Shorten some wording

Author: Matei Zaharia <matei@databricks.com>

Closes #806 from mateiz/doc-update and squashes the following commits:

d9345cd [Matei Zaharia] typo
a179f8d [Matei Zaharia] Tweaks to Mesos docs
SPARK-1864 Look in spark conf instead of system properties when propagating configuration to executors.

Author: Michael Armbrust <michael@databricks.com>

Closes #808 from marmbrus/confClasspath and squashes the following commits:

4c31d57 [Michael Armbrust] Look in spark conf instead of system properties when propagating configuration to executors.
Version bump of spark-ec2 scripts

This will allow us to change things in spark-ec2 related to the 1.0 release.

Author: Patrick Wendell <pwendell@gmail.com>

Closes #809 from pwendell/spark-ec2 and squashes the following commits:

59117fb [Patrick Wendell] Version bump of spark-ec2 scripts