Allow "terraform state mv" in pipeline

[kmanning]

• Now that we've got Destroy in place, it opens up a number of interesting opportunities
• What if we implemented terraform state mv the same way we implemented terraform destroy?
• What if we prompted the user for source and destination IDs, and then performed terraform mv with the assistance of all of the existing plugins?

[kmanning]

If we have the Strategy refactoring in v6.0, we could probably do a:

1. plan
2. terraform state mv
3. plan (to confirm your change)

[kmanning]

If you had a bunch of state changes, we could probably even throw the user in an optional loop:

1. Plan
2. terraform state mv
3. plan (to confirm your change)
4. "Do you want to do another state mv on this environment?" Yes? - repeat. No? - move to the next environment.