Added privileged, parameters to DockerInfo proto
Support for docker privileged mode, arbitrary opts

- Added privileged, parameters to
  mesosphere.marathon.state.Container.Docker.
- Added cases to ContainerTest.
- Added explanation of new parameters to
  native-docker.md, example in rest-api.md.
Addressed review comments for #798.

- Encapsulated parameter handling in a function.
- Fixed typos in marathon.proto and docs.
Merge pull request #798 from mesosphere/789-arbitrary-docker-options

789 arbitrary docker options