executor creation failed should not make the worker restart
fix for SPARK-1027

change TestClient & Worker to Some("xxx")

kill manager if it is started

remove unnecessary .get when fetch "SPARK_HOME" values
refactor sparkHome to val

clean code
Merge pull request #447 from CodingCat/SPARK-1027

fix for SPARK-1027

fix for SPARK-1027  (https://spark-project.atlassian.net/browse/SPARK-1027)

FIXES

1. change sparkhome from String to Option(String) in ApplicationDesc

2. remove sparkhome parameter in LaunchExecutor message

3. adjust involved files