Changed cgroups killTasks() sequence.

The sequence is as follows:
  stop -> kill -> empty -> freeze -> kill -> thaw -> empty

We also now ignore ESRCH errors from kill() in cgroups::kill().

Review: https://reviews.apache.org/r/11131
Simplify os::hostname() in libstout.

Review: https://reviews.apache.org/r/11108
Include pre/post-package hook scripts in Hadoop tutorial.

Review: https://reviews.apache.org/r/11110
Allow ending Hadoop tutorial early.

Allow someone to end tutorial after building/packaging complete.  You
can also skip the test part by exporting SKIP_TESTS (i.e., 'make hadoop
SKIP_TESTS=1').

Review: https://reviews.apache.org/r/11111
Check for Python.h in configure script.

Review: https://reviews.apache.org/r/11114
Use more portable paths for tutorial test.

Review: https://reviews.apache.org/r/11115
Fix TaskTracker pending tasks calculation.

Review: https://reviews.apache.org/r/11116
Ignore unhealthy TaskTrackers.

Review: https://reviews.apache.org/r/11117
Be more intelligent about slot allocation.

When we get a resource offer, we'll try to be clever about how we
allocate slots to the offers.  Ideally we want to use as much of the
resources available when we have a lot of pending tasks, and we also
don't want to use more resources than we actually need.

Review: https://reviews.apache.org/r/11118
Don't prematurely kill TaskTrackers.

We assign the JobID to the internal Mesos tracker (for the TaskTracker)
rather than the TaskID.

In the case where a TaskTracker has only map tasks assigned to it and
they have all completed, we mustn't terminate the tracker until the
entire job has finished, including the map tasks.

Review: https://reviews.apache.org/r/11119
Shuffle offers before sending to frameworks.

This helps ensure fair allocation of resources.

Review: https://reviews.apache.org/r/11121
Kill tasks that never properly launch.

After trying to launch a task tracker, we'll wait up to 5 minutes before
giving up and killing the task.

Review: https://reviews.apache.org/r/11124
Allow some JVM memory vars to be configured.

Review: https://reviews.apache.org/r/11130
Don't accept offers on the same host/port.

We'll try to find a port combination that hasn't already been used to
launch a TaskTracker.

Review: https://reviews.apache.org/r/11161/
Write Mesos JobTracker stats to state file.

Review: https://reviews.apache.org/r/11165/
s/hadoopJobs/jobs/g in Hadoop scheduler.

Review: https://reviews.apache.org/r/11489
Refactor Hadoop job completion.

Review: https://reviews.apache.org/r/11603
Stop tracker timer when we terminate tasks.

Review: https://reviews.apache.org/r/11604
Add --enable-debug configure flag.

Review: https://reviews.apache.org/r/11605
Slave ping timeout may be increased by flags.

Review: https://reviews.apache.org/r/12885