When init attempts to install a legacy provider required by state and
fails, but another provider with the same type is successfully
installed, this almost definitely means that the user is migrating an
in-house provider. The solution here is to use the `terraform state
replace-provider` subcommand.
This commit makes that next step clearer, by detecting this specific
case, and displaying a list of commands to fix the existing state
provider references.
Alisdair McDiarmid