Fix discovery managers to be properly cancelled

Signed-off-by: Jinwook Jeong <vustthat@gmail.com>

discovery/legacymanager/manager.go

@@ -140,12 +140,10 @@ type Manager struct {
 // Run starts the background processing
 func (m *Manager) Run() error {
 	go m.sender()
-	for range m.ctx.Done() {
+	<-m.ctx.Done()
 	m.cancelDiscoverers()
 	return m.ctx.Err()
 }
-	return nil
-}
 
 // SyncCh returns a read only channel used by all the clients to receive target updates.
 func (m *Manager) SyncCh() <-chan map[string][]*targetgroup.Group {

discovery/manager.go

@@ -166,12 +166,10 @@ type Manager struct {
 // Run starts the background processing.
 func (m *Manager) Run() error {
 	go m.sender()
-	for range m.ctx.Done() {
+	<-m.ctx.Done()
 	m.cancelDiscoverers()
 	return m.ctx.Err()
 }
-	return nil
-}
 
 // SyncCh returns a read only channel used by all the clients to receive target updates.
 func (m *Manager) SyncCh() <-chan map[string][]*targetgroup.Group {