bootstrap needs environment config

[William Reade]

As it is, initzk takes --instance-id and --env-type (in addition to state info). This is not enough information; while we *could* infer both authorized-keys and default-series from local state on the bootstrap machine, we still don't have the environment name; and we *will* need constraints info stored at bootstrap time as well.

We should drop the --env-type arg and have an --env-config arg, holding a base64-encoded config serialization (with secrets stripped), which should be dumped directly into /environment *before* we write the /initialized node. This also gives us a path for passing things we know we'll need (such as constraints, which will also go in /environment, I think) at bootstrap time, without having to change the bootstrap code again, which is a surprisingly ugly hassle IM(python)E.

[Dave Cheney (dave-cheney)]

I'm respectfully removing myself from this bug (for the moment) as this is not the issue I thought it was. This is not a comment on the importance of this bug, just unrelated to the piece of code I was working which triggered this bug report during review.