add backend.Operation.StateLocker

Add the StateLocker field so that the state lock can be carried between
the different function scopes of the backend code. This will allow the
backend context to lock the state before it's read, while allowing the
different operations to unlock the state when they complete.

backend/backend.go

@@ -9,6 +9,7 @@ import (
 	"errors"
 	"time"
 
+	"github.com/hashicorp/terraform/command/clistate"
 	"github.com/hashicorp/terraform/config/module"
 	"github.com/hashicorp/terraform/state"
 	"github.com/hashicorp/terraform/terraform"
@@ -135,6 +136,10 @@ type Operation struct {
 	// state.Lockers for its duration, and Unlock when complete.
 	LockState bool
 
+	// StateLocker is used to lock the state while providing UI feedback to the
+	// user. This will be supplied by the Backend itself.
+	StateLocker clistate.Locker
+
 	// The duration to retry obtaining a State lock.
 	StateLockTimeout time.Duration