Add a utility to get container name from podoptions

This commit adds a utility in `pod.go` to get us container name from podoptions
so that we can use this while creating the Pod and while getting the logs from
pod and we would get the correct container name that was while creating the pod
.
In the next PRs this utility will be consumed by rest of the code.

pkg/kube/pod.go

@@ -199,6 +199,17 @@ func GetPodObjectFromPodOptions(cli kubernetes.Interface, opts *PodOptions) (*v1
 	return pod, nil
 }
 
+// ContainerNameFromPodOptsOrDefault returns the container name if it's set in
+// the passed `podOptions` value. If not, it's returns the default container
+// name. This should be used whenever we create pods for Kanister functions.
+func ContainerNameFromPodOptsOrDefault(po *PodOptions) string {
+	if po.ContainerName != "" {
+		return po.ContainerName
+	}
+
+	return defaultContainerName
+}
+
 // CreatePod creates a pod with a single container based on the specified image
 func CreatePod(ctx context.Context, cli kubernetes.Interface, opts *PodOptions) (*v1.Pod, error) {
 	pod, err := GetPodObjectFromPodOptions(cli, opts)

pkg/kube/pod_test.go

@@ -881,3 +881,27 @@ func (s *PodSuite) TestSetLifecycleHook(c *C) {
 	c.Assert(err, IsNil)
 	c.Assert(pod.Spec.Containers[0].Lifecycle, DeepEquals, lch)
 }
+
+func (s *PodControllerTestSuite) TestContainerNameFromPodOptsOrDefault(c *C) {
+	for _, tc := range []struct {
+		podOptsContainerName  string
+		expectedContainerName string
+	}{
+		{
+			podOptsContainerName:  "conone",
+			expectedContainerName: "conone",
+		},
+		{
+			podOptsContainerName:  "",
+			expectedContainerName: defaultContainerName,
+		},
+	} {
+		name := ContainerNameFromPodOptsOrDefault(&PodOptions{
+			ContainerName: tc.podOptsContainerName,
+		})
+		c.Assert(name, Equals, tc.expectedContainerName)
+	}
+
+	name := ContainerNameFromPodOptsOrDefault(&PodOptions{})
+	c.Assert(name, Equals, defaultContainerName)
+}