Fixed scheduler driver to call disconnected() when master fails over.

Review: https://reviews.apache.org/r/11191
Fixed master to send a FrameworkReregistered message when the
framework re-registers with a failed over master.

Review: https://reviews.apache.org/r/11348
Simplify os::hostname() in libstout.

Review: https://reviews.apache.org/r/11108
Run Hadoop tutorial binaries from within build dir.

Review: https://reviews.apache.org/r/11109
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
Use XZ (LZMA) for package on Linuxes.

Review: https://reviews.apache.org/r/11112
Build fix for HadoopPipes.cc with GCC 4.7.

Review: https://reviews.apache.org/r/11113
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
Hadoop tutorial version bump (CDH4.2.0 -> 4.2.1).

Review: https://reviews.apache.org/r/11120
Shuffle offers before sending to frameworks.

This helps ensure fair allocation of resources.

Review: https://reviews.apache.org/r/11121
Slave feature: maximum system load.

When the load exceeds a specified value, don't accept tasks.  Some nodes
may become unstable under excessive load (i.e., heavy disk I/O), and
this helps prevent the assigning of further tasks to busy slaves.

Review: https://reviews.apache.org/r/11122
Log executor output to syslog.

Review: https://reviews.apache.org/r/11123
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
Terminate executors that aren't needed.

If we launch an executor and then kill the task immediately after, make
sure we also terminate the executor when there are no other tasks.

Review: https://reviews.apache.org/r/11125