Add worker labels for the machine deployments

We are missing worker labels and this may lead to
future problems when we will want to scale, wrong nodes
can be chosen for the worker MachineDeployments.

This is a temporary solution to add this to kustomize
Permanent solution should add labels to host generation
and variable catalogue.

Relates-To: #531

Change-Id: Ia07f1d9125bf5b6aadea3750ea53bc34228577ca

manifests/site/test-site/target/workers/nodes/kustomization.yaml

@@ -5,4 +5,4 @@ generators:
   - ../hostgenerator
 
 commonLabels:
-  airshipit.org/k8s-role: controlplane-host
+  airshipit.org/k8s-role: worker

manifests/site/test-site/target/workers/provision/metal3machinetemplate.yaml

@@ -5,6 +5,9 @@ metadata:
 spec:
   template:
     spec:
+      hostSelector:
+        matchLabels:
+          airshipit.org/k8s-role: worker
       image:
         url: http://10.23.24.102:80/images/data-plane.qcow2
         checksum: http://10.23.24.102:80/images/data-plane.qcow2.md5sum