Move env var code into its own package

This creates a new package -- podutils. The env var related code
doesn't really have any business being part of the node package,
and to create a separation of concerns, faster tests, and just
general code isolation and cleanliness, we can move the env
var related code into this package. This change is purely hygiene,
and not logic related.

For node, the package is under internal, because the constructor
references manager, which is an internal package.

node/pod.go

@@ -21,6 +21,7 @@ import (
 
 	"github.com/google/go-cmp/cmp"
 	pkgerrors "github.com/pkg/errors"
+	"github.com/virtual-kubelet/virtual-kubelet/internal/podutils"
 	"github.com/virtual-kubelet/virtual-kubelet/log"
 	"github.com/virtual-kubelet/virtual-kubelet/trace"
 	corev1 "k8s.io/api/core/v1"
@@ -68,7 +69,7 @@ func (pc *PodController) createOrUpdatePod(ctx context.Context, pod *corev1.Pod)
 
 	// We do this so we don't mutate the pod from the informer cache
 	pod = pod.DeepCopy()
-	if err := populateEnvironmentVariables(ctx, pod, pc.resourceManager, pc.recorder); err != nil {
+	if err := podutils.PopulateEnvironmentVariables(ctx, pod, pc.resourceManager, pc.recorder); err != nil {
 		span.SetStatus(err)
 		return err
 	}