Mesos 0.17.0 support.

The issues with supporting Mesos 0.17.0 are related to incompatible old dependencies. The resolution consisted in:

- Bumping the Mesos version from ```0.14.0-RC4``` to ```0.17.0```.
- Bumping the Google Protobuf version from ```2.4.1``` to ```2.5.1```.