Update the command package to use the new module storage. Move the old
command output strings into the module storage itself. This could be
moved back later either by using ui callbacks, or designing a module
storage interface once we know what the final requirements will look
like.
Previously we were using fmt.Sprintf and thus forcing the stringification
of the wrapped error.
Using errwrap allows us to unpack the original error at the top of the
stack, which is useful when the wrapped error is really a hcl.Diagnostics
containing potentially-multiple errors and possibly warnings.
Instead of providing the a path in BackendOpts, provide a loaded
*config.Config instead. This reduces the number of places where
configuration is loaded.
James Bardin