SPARK-884: Add unit test to validate Spark JSON output

This unit test simply validates that the outputs of
the JsonProtocol methods are syntactically valid JSON.
Updating assembly README to reflect recent changes in the build.
Merge pull request #894 from c0s/master

Updating assembly README to reflect recent changes in the build.
Address Patrick's comments
Fix line over 100 chars
Merge pull request #893 from ilikerps/master

SPARK-884: Add unit test to validate Spark JSON output
Fix bug SPARK-864
SPARK-821: Don't cache results when action run locally on driver

Caching the results of local actions (e.g., rdd.first()) causes the driver to
store entire partitions in its own memory, which may be highly constrained.
This patch simply makes the CacheManager avoid caching the result of all locally-run computations.
Add unit test and address comments
Merge pull request #891 from xiajunluan/SPARK-864

[SPARK-864]DAGScheduler Exception if we delete Worker and StandaloneExecutorBackend then add Worker
Reynold's second round of comments
Merge pull request #895 from ilikerps/821

SPARK-821: Don't cache results when action run locally on driver
Hot fix to resolve the compilation error caused by SPARK-821.
Provide docs to describe running on CDH/HDP cluster.

This doc consolidates information relevant to CDH/HDP users in a single place.