Istio integration (#421)

This the very first step for fission to integrate with Istio, which is an open platform to connect, manage, and secure microservices. With Istio, users are able to monitor functions usage and trace requests latency through dashboards. For more information, please visit http://fission.io/docs/

executor/poolmgr/gpm.go

@@ -151,11 +151,14 @@ func (gpm *GenericPoolManager) CleanupPools(envs []crd.Environment) {
 func (gpm *GenericPoolManager) eagerPoolCreator() {
 	pollSleep := time.Duration(2 * time.Second)
 	for {
-		time.Sleep(pollSleep)
-
 		// get list of envs from controller
 		envs, err := gpm.fissionClient.Environments(metav1.NamespaceAll).List(metav1.ListOptions{})
 		if err != nil {
+			if fission.IsNetworkError(err) {
+				log.Printf("Encountered network error, retrying: %v", err)
+				time.Sleep(5 * time.Second)
+				continue
+			}
 			log.Fatalf("Failed to get environment list: %v", err)
 		}
 
@@ -176,6 +179,7 @@ func (gpm *GenericPoolManager) eagerPoolCreator() {
 
 		// Clean up pools whose env was deleted
 		gpm.CleanupPools(envs.Items)
+		time.Sleep(pollSleep)
 	}
 }