Retrieve pod metrics only if metrics server is running and Go lint fixes (#2094)

* Retrieve pod metrics only if metrics server is running

Currently we query pod metrics every 30 sec which floods executor logs,
added check which confirms if metrics server is running then only we start
querying pod metrics for identifying CPU utilization.

Signed-off-by: Sanket Sudake <sanketsudake@gmail.com>

* Fixed couple of typos and misspells with Go CI

Signed-off-by: Sanket Sudake <sanketsudake@gmail.com>

* Remove unnecessary conversions with Go CI

Signed-off-by: Sanket Sudake <sanketsudake@gmail.com>

pkg/utils/informer.go

@@ -1,12 +1,14 @@
 package utils
 
 import (
-	v1 "github.com/fission/fission/pkg/apis/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/labels"
 	"k8s.io/apimachinery/pkg/selection"
 	k8sInformers "k8s.io/client-go/informers"
 	"k8s.io/client-go/kubernetes"
+	metricsapi "k8s.io/metrics/pkg/apis/metrics"
+
+	v1 "github.com/fission/fission/pkg/apis/core/v1"
 )
 
 func GetInformerFacoryByExecutor(client *kubernetes.Clientset, executorType v1.ExecutorType) (k8sInformers.SharedInformerFactory, error) {
@@ -22,3 +24,22 @@ func GetInformerFacoryByExecutor(client *kubernetes.Clientset, executorType v1.E
 		}))
 	return informerFactory, nil
 }
+
+func SupportedMetricsAPIVersionAvailable(discoveredAPIGroups *metav1.APIGroupList) bool {
+	var supportedMetricsAPIVersions = []string{
+		"v1beta1",
+	}
+	for _, discoveredAPIGroup := range discoveredAPIGroups.Groups {
+		if discoveredAPIGroup.Name != metricsapi.GroupName {
+			continue
+		}
+		for _, version := range discoveredAPIGroup.Versions {
+			for _, supportedVersion := range supportedMetricsAPIVersions {
+				if version.Version == supportedVersion {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}