PortMapping: allow containers to recover even when they were not
managed by Network Isolator previously.

This eases deployment where a slave could be upgraded to use Network
Isolator without removing all the existing tasks.

- Added a new test.
- Moved all portmapping tests to a new file.

Review: https://reviews.apache.org/r/23214
Minor fix to mesos_tests_SOURCES in Makefile.am
Adds collectd plugin to Mesos tools documentation.
HTTP Authenticated '/shutdown' endpoint.

Review: https://reviews.apache.org/r/22832
Fixed the recovery timeout in the tests.
Fixed health check command subprocess handling.

Currently it doesn't check all subprocess future states, and also
creates a pipe to stdin which can cause some scripts to expect stdin
input and blocks.

Review: https://reviews.apache.org/r/23416
Add Sailthru to the "Powered by Mesos" page.

This closes: #21
Review: https://github.com/apache/mesos/pull/21
Added CHANGELOG for 0.19.1.
Updated the upgrades document for 0.18.2 and 0.19.1.
Added logging to vote.sh to help debug a confusing exit.
Unbundled picojson

Enable mesos to build against the system installed version of picojson.

Review: https://reviews.apache.org/r/23091
Unbundled libev

Enable mesos to build against the system installed version of libev.

Review: https://reviews.apache.org/r/23414
Added 'bool' return value to Containerizer::launch.
Added composing containerizer and --containerizers flag.
Added a 'Docker' abstraction.
Added a Docker containerizer.
Bug fixes and cleanups in Docker abstraction.
Integrated DockerContainerizer.
Add environment test for Docker.

Review: https://reviews.apache.org/r/23490
Added pid() in docker/docker.cpp to get the pid of the container.