Unified Containerizer

[kszucs]

Added support for unified containerizer

Motivation and Context

New release of mesos makes this possible. Better resource isolation, executor can be reused.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [x] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have read the CONTRIBUTING document.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.

Review:

• [ ] @tdna approved
• [ ] @lazerviking assignee approved