Move kubeconfig utility to a shared pkg

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>

internal/kubeconfig/currentcontext.go

@@ -0,0 +1,17 @@
+package kubeconfig
+
+// GetCurrentContext returns "current-context" value in given
+// kubeconfig object Node, or returns "" if not found.
+func (k *Kubeconfig) GetCurrentContext() string {
+	v := valueOf(k.rootNode, "current-context")
+	if v == nil {
+		return ""
+	}
+	return v.Value
+}
+
+func (k *Kubeconfig) UnsetCurrentContext() error {
+	curCtxValNode := valueOf(k.rootNode, "current-context")
+	curCtxValNode.Value = ""
+	return nil
+}