Add MetricsServlet for Spark metrics system
MetricsServlet code refactor according to comments
Merge pull request #784 from jerryshao/dev-metrics-servlet

Add MetricsServlet for Spark metrics system
Slight change to pr-784
Merge pull request #817 from pwendell/pr_784

Minor clean-up in metrics servlet code
Properly account for killed tasks.

The TaskState class's isFinished() method didn't return true for
KILLED tasks, which means some resources are never reclaimed
for tasks that are killed. This also made it inconsistent with the
isFinished() method used by CoarseMesosSchedulerBackend.
Reuse the set of failed states rather than creating a new object each time
Print run command to stderr rather than stdout
Merge pull request #818 from kayousterhout/killed_fix

Properly account for killed tasks.
Merge pull request #821 from pwendell/print-launch-command

Print run command to stderr rather than stdout
Bug fix for display of shuffle read/write metrics.

This fixes an error where empty cells are missing if a given task
has no shuffle read/write.
Capturing GC detials in TaskMetrics
Correct sorting order for stages
Correcting terminology in RDD page
Small style clean-up
Update to Mesos 0.12.1
Merge pull request #824 from mateiz/mesos-0.12.1

Update to Mesos 0.12.1
Set SPARK_CLASSPATH for maven repl tests
Merge pull request #825 from shivaram/maven-repl-fix

Set SPARK_CLASSPATH for maven repl tests
Fixed 2 bugs in executor UI.

1) UI crashed if the executor UI was loaded before any tasks started.
2) The total tasks was incorrectly reported due to using string (rather
than int) arithmetic.