Proposal: Swarm use unreserved/reserved resources from Mesos

[ghost]

When launch tasks, Swarm only use unreserved resource; and if Mesos offer reserved resources, the role info are also ignored which is rejected by Mesos master.

This proposal is to let Swarm use both un-reserved/reserved resources Mesos.

[ghost]

@jimenez any comments on this requirement?

[gradywang]

Append the PR #1890 , In that PR, Swarm is enabled to use both reserved and unreserved resources to create container.

The design proposal is : swarm will use reserved resources firstly, if reserved resources are not enough for the creating container, then the unreserved resources will be used for the gap. This behaviour could eventually be configurable by end user (use unreserved resources or reserved resources firstly), although we may want to avoid providing that option until we see a valid use case.

@jimenez , cloud you help to review this proposal and that patch? Thanks!

[nishanttotla]

Closing due to #2853