configbox: external provisioner kickoff (knife-solo / knife-zero)

[darkn3rd]

Motivation

knife-solo and knife-zero can kick off provisioning externally (from the host, controlling the guest remotely) rather than using Vagrant's own built-in Chef provisioner. configbox/legacy/knife-solo is prior art for the old workflow. Not yet clear how this should integrate with #21 (chef_solo) and #22 (chef_zero)'s own modernized versions.

Design

Open for now - the concrete requirement is that whatever shared logic exists between knife-solo/knife-zero's external-kickoff approach and #21/#22's own provisioning should actually be shared, not duplicated into three separate implementations of "install this cookbook onto this box."

Open questions

• Does external kickoff replace Vagrant's built-in provisioner for chef_solo/chef_zero entirely, or exist as an alternative path alongside it?
• What's actually reusable between the two knife variants and configbox: modernize chef_solo provisioner (Cinc) #21/configbox: modernize chef_zero provisioner (Cinc, in-memory simulated server) #22 - the cookbooks themselves (most likely), or also some wrapper/invocation logic?

Out of scope for now

Depends on #21/#22 having working initial versions first.