Updated Mesos codebase to set the framework principal in FrameworkInfo.

Review: https://reviews.apache.org/r/22315
Add Apache Hama to list of Mesos frameworks.
Change MesosContainerizer::update to not return failure for unknown container.

Review: https://reviews.apache.org/r/22252
post-reviews.py: compatible with git previous to 1.7.2.

The %B formatter introduced in git 1.7.2 while only git 1.7.1
available in RHEL 6.3 release, which is still a widely used release.

Review: https://reviews.apache.org/r/22405
Switched to subprocess.Popen to get stdout streamed from
verify-reviews.

Using Popen instead of check_output means that the output is streamed
to the console. As such, runs that timeout will still include partial
logs enabling us to debug any issues.

Review: https://reviews.apache.org/r/22422
Initial import for health check
Fixed Protobuf to JSON serialization of optional fields with default values.

Previously, only optional fields which where explicitly set would be serialized regardless whether default values was present.
This patch adds those fields explicitly.

Review: https://reviews.apache.org/r/21246
Cleaned up JSON work
Snapshot of current health check program.
Add task health check