[swarm_docker] Clean up a bunch of vet/lint warnings.

Change-Id: I635ab25b7c38d0c9e58de34753497e54667c9fcf
diff --git a/cmd/swarm_docker/swarm_docker.go b/cmd/swarm_docker/swarm_docker.go
index f427b10..28ddf29 100644
--- a/cmd/swarm_docker/swarm_docker.go
+++ b/cmd/swarm_docker/swarm_docker.go
@@ -88,10 +88,10 @@
 		Target   string `json:"target"`
 		ReadOnly bool   `json:"readonly,omitempty"`
 	} `json:"mounts,omitempty"`
-	hostname   string `json:"-"`
-	domainname string `json:"-"`
-	cpuset     string `json:"-"`
-	memory     int    `json:"-"`
+	hostname   string
+	domainname string
+	cpuset     string
+	memory     int
 }
 
 // stringsFlag implements flag.Value interface for array of strings.
@@ -161,7 +161,7 @@
 
 	var wg sync.WaitGroup
 	p.lock.RLock()
-	for id, _ := range p.containers {
+	for id := range p.containers {
 		wg.Add(1)
 		go func(id string) {
 			defer wg.Done()
@@ -229,7 +229,7 @@
 
 	var wg sync.WaitGroup
 	errc := make(chan error)
-	for id, _ := range p.containers {
+	for id := range p.containers {
 		wg.Add(1)
 		go func(id string) {
 			defer wg.Done()
@@ -261,7 +261,7 @@
 
 	var wg sync.WaitGroup
 	errc := make(chan error)
-	for id, _ := range p.containers {
+	for id := range p.containers {
 		wg.Add(1)
 		go func(id string) {
 			defer wg.Done()
@@ -369,7 +369,7 @@
 	})
 	summary, err := r.client.ImageList(ctx, types.ImageListOptions{Filters: filters})
 	if err != nil {
-		return fmt.Errorf("cannot list images: %v\n", err)
+		return fmt.Errorf("cannot list images: %v", err)
 	}
 	if len(summary) != 0 {
 		return nil
@@ -404,7 +404,7 @@
 
 	type JSONMessage struct {
 		Status   string `json:"status,omitempty"`
-		Progress string `json:serror,omitempty"`
+		Progress string `json:"serror,omitempty"`
 		Error    string `json:"error,omitempty"`
 	}
 
@@ -433,9 +433,8 @@
 	strs := strings.SplitN(hostname, ".", 2)
 	if len(strs) == 2 {
 		return strs[0], strs[1], nil
-	} else {
-		return strs[0], "", nil
 	}
+	return strs[0], "", nil
 }
 
 // loadConfig reads the service configuration from a file.
@@ -578,13 +577,14 @@
 			}
 			break loop
 		case <-interrupts:
-			cancel()
 			break loop
 		case err := <-errs:
 			log.Printf("error in the pool: %v", err)
 		}
 	}
 
+	cancel()
+
 	// Let systemd know that we began to shutdown.
 	if _, err := sdNotify(false, "STOPPING=1"); err != nil {
 		log.Printf("failed to notify systemd: %v", err)