Fix master-node only graph processing

Check for nodes list emptiness when discovering
online nodes. With master-only graph we do not have
any nodes except for virtual_sync_node and master.
This leads to failure of mcollective discover
as it receives an empty list

Change-Id: I38bfd9b98f79ba83527de5956b66d2fc3ddb0020
Closes-bug: #1590337

lib/astute/task_deployment.rb

@@ -234,23 +234,25 @@ module Astute
       uids.delete('virtual_sync_node')
       # In case of big amount of nodes we should do several calls to be sure
       # about node status
-      Astute.config.mc_retries.times.each do
-        systemtype = Astute::MClient.new(
-          @ctx,
-          "systemtype",
-          uids,
-          _check_result=false,
-          10
-        )
-        available_nodes = systemtype.get_type.select do |node|
-          node.results[:data][:node_type].chomp == "target"
+      if !uids.empty?
+        Astute.config.mc_retries.times.each do
+          systemtype = Astute::MClient.new(
+              @ctx,
+              "systemtype",
+              uids,
+              _check_result=false,
+              10
+          )
+          available_nodes = systemtype.get_type.select do |node|
+            node.results[:data][:node_type].chomp == "target"
+          end
+
+          available_uids += available_nodes.map { |node| node.results[:sender] }
+          uids -= available_uids
+          break if uids.empty?
+
+          sleep Astute.config.mc_retry_interval
         end
-
-        available_uids += available_nodes.map { |node| node.results[:sender] }
-        uids -= available_uids
-        break if uids.empty?
-
-        sleep Astute.config.mc_retry_interval
       end
 
       Astute.logger.warn "Offline node #{uids}" if uids.present?

spec/unit/task_deployment_spec.rb

@@ -67,6 +67,20 @@ describe Astute::TaskDeployment do
     }
   end
 
+  let(:tasks_graph_2) do
+    {"master"=>
+         [{
+              "type"=>"noop",
+              "fail_on_error"=>true,
+              "required_for"=>[],
+              "requires"=> [],
+              "id"=>"ironic_post_swift_key",
+              "parameters"=>{},
+          }],
+     "null"=> []
+    }
+  end
+
   let(:tasks_directory) do
     {"ironic_post_swift_key"=>{
       "parameters"=>{
@@ -148,6 +162,20 @@ describe Astute::TaskDeployment do
         tasks_directory: tasks_directory)
     end
 
+    it 'should not fail if there are no nodes to check for offline nodes' do
+      Astute::TaskPreDeploymentActions.any_instance.stubs(:process)
+      task_deployment.stubs(:write_graph_to_file)
+      ctx.stubs(:report)
+
+      task_deployment.expects(:fail_offline_nodes).returns([])
+
+      Astute::TaskCluster.any_instance.stubs(:run).returns({:success => true})
+      task_deployment.deploy(
+          tasks_metadata: tasks_metadata,
+          tasks_graph: tasks_graph_2,
+          tasks_directory: tasks_directory)
+    end
+
     it 'should setup stop condition' do
       Astute::TaskPreDeploymentActions.any_instance.stubs(:process)
       task_deployment.stubs(:write_graph_to_file)