Add API to help schedule next test run

[bassosimone]

Related to the M-Lab six hours incident. Suggested by @mattmathis and @gfr10598.

BTW, there is code for doing that in the ndt7 spec.

Moved here from measurement-kit/engine#8

[gfr10598]

New idea - I think mlab-ns should return this as part of its response. Then we will have more influence over this on the server side, and can make adjustments, for example, in response to load.

[pboothe]

@gfr10598 and @stephen-soltesz want to talk about the right path forward here.

[mattmathis]

This makes sense if there as also an easy way to ask for just the recommended schedule, w/o asking for current servers. Should the recommended time depend on the precise query?

Please include me in the conversation.

[bassosimone]

I'm increasingly inclined to believe that we should not add this feature to this client and that (1) we should document the best practices and (2) leverage mlab-ns as @gfr10598 suggests.

Unless there are objections, I'd like to close this issue in a week or so.

[stephen-soltesz]

@bassosimone I've migrated this issue to the mlab-ns repo since the desire sounds like we want some mlab-ns support for scheduling.