Fix extra space in fetcher code.
Fixed coding style issue in Node class

Removed the space between & and the parameter type

Review: https://reviews.apache.org/r/28382
Expanded labels comment in mesos.proto.

Review: https://reviews.apache.org/r/28444
Adds Coursera to Mesos adopters list.
Rename Socket::read to Socket::recv.

This is more consistent: send/recv vs. send/read.

Review: https://reviews.apache.org/r/28484
Renamed poll.cpp to libev_poll.cpp.

Review: https://reviews.apache.org/r/28314
Extended install() to support more arguments.

Review: https://reviews.apache.org/r/28363
Refactored task launching in the master.

This adds addTask(), which is similar to addSlave() and addFramework().
The benefit is that we allow the caller to add the task and have control
over when the RunTaskMessage is sent.

Review: https://reviews.apache.org/r/28364
Fixed a double counting bug for staging tasks.

Review: https://reviews.apache.org/r/28433
Removed the empty resource check in master.

Review: https://reviews.apache.org/r/28616
Add slave id to docker container name prefix.
Add option to disable docker containerizer killing orphans
Add executor for docker containerizer
Integrate docker executor into containerizer.
Re-enable docker recover test.
Add docker_mesos_image flag to slave flags.
Add docker_sock to slave flags
Add option to launch docker containers with helper containers.