Proposal: Add support for maintenance api in next branch

[cinchurge]

As it currently stands, the next branch doesn't appear to support the maintenance api, which is actually urgently needed by our team. Is this something on the roadmap? Or can we contribute to this effort?

[jdef]

several people have asked about the operator API, so there's definitely community interest here. I'd love to see operator API support in the Mesos v1 ("next") binding

[jdef]

xref #275