SPARK-1337: Application web UI garbage collects newest stages

Simple fix...

Author: Patrick Wendell <pwendell@gmail.com>

Closes #320 from pwendell/stage-clean-up and squashes the following commits:

29be62e [Patrick Wendell] SPARK-1337: Application web UI garbage collects newest stages instead old ones
SPARK-1350. Always use JAVA_HOME to run executor container JVMs.

Author: Sandy Ryza <sandy@cloudera.com>

Closes #313 from sryza/sandy-spark-1350 and squashes the following commits:

bb6d187 [Sandy Ryza] SPARK-1350. Always use JAVA_HOME to run executor container JVMs.
Merge remote-tracking branch 'upstream/master' into spark-1403