Implement shutting down status

pkg/instance/status.go

@@ -14,6 +14,7 @@ const (
 	Running
 	Failed
 	Restarting
+	ShuttingDown
 )
 
 var nameToStatus = map[string]Status{
@@ -21,6 +22,7 @@ var nameToStatus = map[string]Status{
 	"running":       Running,
 	"failed":        Failed,
 	"restarting":    Restarting,
+	"shutting_down": ShuttingDown,
 }
 
 var statusToName = map[Status]string{
@@ -28,6 +30,7 @@ var statusToName = map[Status]string{
 	Running:      "running",
 	Failed:       "failed",
 	Restarting:   "restarting",
+	ShuttingDown: "shutting_down",
 }
 
 // Status enum JSON marshaling methods