Rework the findAll to support label expressions

Signed-off-by: Jose Luis Rivero <jrivero@honurobotics.com>

jenkins-scripts/tools/label-assignment-backstop.groovy

@@ -48,18 +48,16 @@ for (tup in exactly_one_labels) {
     println("No online host currently has the label ${nightly_label}")
     println("Appointing a node from the configured pool matching '${pool_label}'")
 
-    def node_pool = Jenkins.instance.nodes.findAll { node ->
+    def node_pool = Label.get(pool_label).getNodes().findAll { node ->
       node.toComputer()?.isOnline() &&
-      node.getLabelString().contains(pool_label) &&
       !node.getLabelString().contains(nightly_label_prefix) &&
       !node.getLabelString().contains("test-instance")
     }
 
     if (node_pool.size() <= 0) {
       println("The Pool of '${pool_label}' machines for ${nightly_label} is empty. Reusing a node:")
-      node_pool = Jenkins.instance.nodes.findAll { node ->
+      node_pool =  Label.get(pool_label).getNodes().findAll { node ->
         node.toComputer()?.isOnline() &&
-        node.getLabelString().contains(pool_label) &&
         !node.getLabelString().contains("test-instance")
       }
     }