Most of the state package has been deprecated by the states package.
This PR replaces all the references to the old state package that
can be done simply - the low-hanging fruit.
* states: move state.Locker to statemgr
The state.Locker interface was a wrapper around a statemgr.Full, so
moving this was relatively straightforward.
* command: remove unnecessary use of state package for writing local terraform state files
* move state.LocalState into terraform package
state.LocalState is responsible for managing terraform.States, so it
made sense (to me) to move it into the terraform package.
* slight change of heart: move state.LocalState into clistate instead of
terraform
This work was done against APIs that were already changed in the branch
before work began, and so it doesn't apply to the v0.12 development work.
To allow v0.12 to merge down to master, we'll revert this work out for now
and then re-introduce equivalent functionality in later commits that works
against the new APIs.