builder/digitalocean: properly cleanup goroutines for status checking

builder/digitalocean/wait.go

@@ -9,6 +9,9 @@ import (
 // waitForState simply blocks until the droplet is in
 // a state we expect, while eventually timing out.
 func waitForDropletState(desiredState string, dropletId uint, client *DigitalOceanClient, timeout time.Duration) error {
+	done := make(chan struct{})
+	defer close(done)
+
 	result := make(chan error, 1)
 	go func() {
 		attempts := 0
@@ -29,6 +32,15 @@ func waitForDropletState(desiredState string, dropletId uint, client *DigitalOce
 
 			// Wait 3 seconds in between
 			time.Sleep(3 * time.Second)
+
+			// Verify we shouldn't exit
+			select {
+			case <-done:
+				// We finished, so just exit the goroutine
+				return
+			default:
+				// Keep going
+			}
 		}
 	}()