add Python streaming tests
Make setting configs more user-friendly

Previously there were tons of flags that the user must set, and
these are scattered throughout the config.py file. This commit
organizes the necessary settings by category and moves the
important ones to the top.

It also replaces all "SKIP_*" flags with the positive form,
which makes it more straightforward for the user to reason about.
Always rsync Spark to all nodes

When a Worker config changes, for instance, we need to manually
rsync Spark before running spark-perf. With this commit this is
no longer the case.
Ignore results directory
Actually skip PySpark tests if they are not configured to run
Merge pull request #20 from davies/streaming

add Python streaming tests
Add header to result file to explain what the numbers mean

It was very confusing before. For each test all we see is something
like 10.1, 0.25, 9.75, 10.8, 10.35. Every time I have to dig into
the code to figure out what these mean. This commit adds a header to
the result file to explain this.
Rewrite README; add bin/spark-ec2/install-maven script.
Add support for Yarn

This is almost trivial. The only thing we need is to set
SPARK_CLUSTER_URL to "yarn", and avoid restarting the standalone
cluster as we normally do
Support running on Mesos