Revert "Update kubernetes-dashboard version"

dashboard has a limited number of versions and version of k8s can't be used for dashboard as well.
separate variable with version is required for dashboard.

This reverts commit a167729.

Closes-Bug: #1798923
Change-Id: I4c46c925fc338cd9bbf43e4fd6d01cd07eb2afb1

playbooks/roles/k8s/templates/k8s-dashboard.yaml.j2

@@ -13,6 +13,7 @@
 # limitations under the License.
 
 # Configuration to deploy release version of the Dashboard UI compatible with
+# Kubernetes 1.8.
 #
 # Example usage: kubectl create -f <this_file>
 
@@ -114,7 +115,7 @@ spec:
       hostNetwork: true
       containers:
       - name: kubernetes-dashboard
-        image: k8s.gcr.io/kubernetes-dashboard-amd64:{{ k8s_version }}
+        image: k8s.gcr.io/kubernetes-dashboard-amd64:v1.8.3
         ports:
         - containerPort: 8443
           protocol: TCP