fixing typo in conf/slaves

This reverts commit 230ab272, reversing
changes made to 659553b2.

Updated json output to allow for display of worker state

Rename `memoryBytesToString` and `memoryMegabytesToString`

Fix PySpark unit tests on Python 2.6

These are used all over the place now and they are not specific to memory at all.

memoryBytesToString --> bytesToString
memoryMegabytesToString --> megabytesToString

Various UI improvements.

Ops teams need to ensure that the cluster is functional and performant.  Having to scrape the html source for worker state won't work reliably, and will be slow.  By exposing the state in the json output, ops teams are able to ensure a fully functional environment by querying for the json output and parsing for dead nodes.

A few small scheduler / job description changes.

1. Renamed SparkContext.addLocalProperty to setLocalProperty. And allow this function to unset a property.

2. Renamed SparkContext.setDescription to setCurrentJobDescription.

3. Throw an exception if the fair scheduler allocation file is invalid.

Adding GC Stats to TaskMetrics (and three small fixes)

Fixed 2 bugs in executor UI (incl. SPARK-877)

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.

Set SPARK_CLASSPATH for maven repl tests

Update to Mesos 0.12.1

This fixes an error where empty cells are missing if a given task
has no shuffle read/write.

Print run command to stderr rather than stdout

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.

Minor clean-up in metrics servlet code

Add MetricsServlet for Spark metrics system

Simple PageRank algorithm implementation in Python for SPARK-760

Implementing SPARK-865: Add the equivalent of ADD_JARS to PySpark

Now ADD_FILES uses a comma as file name separator.

Create SparkContext in beforeAll for MLLib tests