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
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/
Pretty-print resource type with parsing error.

Review: https://reviews.apache.org/r/11486
Use string comparison for TaskID.

Review: https://reviews.apache.org/r/11488
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
Increase slave timeout.

Review: https://reviews.apache.org/r/11606
Use XZ (LZMA) for package on Linuxes.

Review: https://reviews.apache.org/r/11112
Turn down noise from ZooKeeper.

Review: https://reviews.apache.org/r/11127
Fix hadoop 0.20.205.0 dist.

Review: https://reviews.apache.org/r/11662
Fix executor IDs in web UI.

Some frameworks don't report an executor ID, but have a task ID. As a
workaround, we can use the task ID when the executor ID is empty.

Review: https://reviews.apache.org/r/11814
Allow specification of mininum slot count.

To ensure Hadoop jobs begin promptly, we can specify a minimum number of
'hot slots' to be available for use.  This addresses the TaskTracker
spin up delay that exists with Hadoop on Mesos.  This can be a nuisance
with lower latency applications, such as ad-hoc Hive queries.