* Add support for scoped resources
* refactor existing checks addrs and add check block addr
* Add configuration for check blocks
* introduce check blocks into the terraform node and transform graph
* address comments
* address comments
* don't execute checks during destroy operations
* don't even include check nodes for destroy operations
The checks.Checks type aims to encapsulate keeping track of check results
during a run and then reporting on them afterwards even if the run was
aborted early for some reason.
The intended model here is that each new run starts with an entirely fresh
checks.Checks, with all of the statuses therefore initially unknown, and
gradually populates the check results as we walk the graph in Terraform
Core. This means that even if we don't complete the run due to an error
or due to targeting options we'll still report anything we didn't visit
yet as unknown.
This commit only includes the modeling of checks in the checks package.
For now this is just dead code, and we'll wire it in to Terraform Core in
subsequent commits.
