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
Make sure you clean up the cgroups test.

Sometimes the cgroup test fails because the directory is already there.
This should ensure that it gets cleanup up in that case before we exit.

Review: https://reviews.apache.org/r/11126
Turn down noise from ZooKeeper.

Review: https://reviews.apache.org/r/11127
More cgroup killTask() logging.

Review: https://reviews.apache.org/r/11129
Increase JVM memory overhead.

Review: https://reviews.apache.org/r/11130
For cgroups killTasks(): kill, freeze, kill, thaw.

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/
Call `post-reviews' with --guess-fields argument.

But only do so with the initial creation of the review.

Review: https://reviews.apache.org/r/11159
Ignore errors from post-review.

When updating existing reviews, post-review returns errors erroneously.

Review: https://reviews.apache.org/r/11160
Write Mesos JobTracker stats to state file.

Review: https://reviews.apache.org/r/11165/
Fix post-reviews.py url.

Review:
Pretty-print resource type with parsing error.

Review:
Strip spaces and quotes --resources arg.

Review:
Use string comparison for TaskID.
Fixed synchronization bug when waiting for a process.
Don't log every single completed task.

On large jobs (with many thousands of tasks) this can generate an
unreasonable number of log messages.
Enable debug flags when optimizations disabled.