Because the destroy plan only creates the necessary changes for apply to
remove all the resources, it does no reading of resources or data
sources, leading to stale data in the state. In most cases this is not a
problem, but when a provider configuration is using resource values, the
provider may not be able to run correctly during apply. In prior
versions of terraform, the implicit refresh that happened during
`terraform destroy` would update the data sources and remove missing
resources from state as required.

The destroy plan graph has a minimal amount of information, so it is not
feasible to work the reading of resources into the operation without
completely replicating the normal plan graph, and updating the plan
graph and all destroy node implementation is also a considerable amount
of refactoring. Instead, we can run a normal plan which is used to
refresh the state before creating the destroy plan. This brings back
similar behavior to core versions prior to 0.14, and the refresh can
still be skipped using the `-refresh=false` cli flag.

These tests were not previously running a refresh, and hence did not
expect the resources to be read.

get rid of the mutation of the plans.Plan and return values.