Prior to this change, if you ended up with multiple Pulumi SDK
packages loaded side-by-side, we would fail in obscure ways. The
reason for this was that we initialize and store important state
in static variables. In the case that you load the same library
twice, however, you end up with separate copies of said statics,
which means we would be missing engine RPC addresses and so on.
This change adds the ability to recover from this situation by
mirroring the initialized state in process-wide environment
variables. By doing this, we can safely recover simply by reading
them back when we detect that they are missing. I think we can
eventually go even further here, and eliminate the entry point
launcher shim altogether by simply having the engine launch the
Node program with the right environment variables. This would
be a nice simplification to the system (fewer moving pieces).
There is still a risk that the separate copy is incompatible.
Presumably the reason for loading multiple copies is that the
NPM/Yarn version solver couldn't resolve to a shared version.
This may yield obscure failure modes should RPC interfaces change.
Figuring out what to do here is part of pulumi/pulumi#957.
This fixespulumi/pulumi#777 and pulumi/pulumi#1017.
This change adds a new manifest section to the checkpoint files.
The existing time moves into it, and we add to it the version of
the Pulumi CLI that created it, along with the names, types, and
versions of all plugins used to generate the file. There is a
magic cookie that we also use during verification.
This is to help keep us sane when debugging problems "in the wild,"
and I'm sure we will add more to it over time (checksum, etc).
For example, after an up, you can now see this in `pulumi stack`:
```
Current stack is demo:
Last updated at 2017-12-01 13:48:49.815740523 -0800 PST
Pulumi version v0.8.3-79-g1ab99ad
Plugin pulumi-provider-aws [resource] version v0.8.3-22-g4363e77
Plugin pulumi-langhost-nodejs [language] version v0.8.3-79-g77bb6b6
Checkpoint file is /Users/joeduffy/dev/code/src/github.com/pulumi/pulumi-aws/.pulumi/stacks/webserver/demo.json
```
This addresses pulumi/pulumi#628.
