Add --validate-only to openstack overcloud node import

Previously there was 'openstack baremetal instackenv validate' to
quickly validate an environment file.

Much of which is now done in the validate_nodes mistral workflow.  Add a
mode to cease operations after validating the environment file

Note on the backport:
The old command was removed in Queens, so we need to backport this
new flag to fill in the gap. The workflow was introduced in Pike.

Closes-Bug: #1768604
Change-Id: Ie2bfc79b45f4652285718be34a5e07ce5777c60d
(cherry picked from commit ebc64b681c)

tripleoclient/v1/overcloud_node.py

@@ -194,6 +194,10 @@ class ImportNode(command.Command):
                             help=_('Run the pre-deployment validations. These '
                                    'external validations are from the TripleO '
                                    'Validations project.'))
+        parser.add_argument('--validate-only', action='store_true',
+                            default=False,
+                            help=_('Validate the env_file and then exit '
+                                   'without actually importing the nodes.'))
         parser.add_argument('--provide',
                             action='store_true',
                             help=_('Provide (make available) the nodes'))
@@ -213,6 +217,10 @@ class ImportNode(command.Command):
 
         nodes_config = oooutils.parse_env_file(parsed_args.env_file)
 
+        if parsed_args.validate_only:
+            return baremetal.validate_nodes(self.app.client_manager,
+                                            nodes_json=nodes_config)
+
         if parsed_args.no_deploy_image:
             deploy_kernel = None
             deploy_ramdisk = None

tripleoclient/workflows/baremetal.py

@@ -18,6 +18,36 @@ from tripleoclient import exceptions
 from tripleoclient.workflows import base
 
 
+def validate_nodes(clients, **workflow_input):
+    """Node Registration or Update
+
+    Run the tripleo.baremetal.v1.validate_nodes Mistral workflow.
+    """
+
+    workflow_client = clients.workflow_engine
+    tripleoclients = clients.tripleoclient
+
+    with tripleoclients.messaging_websocket() as ws:
+        execution = base.start_workflow(
+            workflow_client,
+            'tripleo.baremetal.v1.validate_nodes',
+            workflow_input=workflow_input
+        )
+
+        for payload in base.wait_for_messages(workflow_client, ws, execution):
+            if 'message' in payload:
+                print(payload['message'])
+
+    if payload['status'] == 'SUCCESS':
+        print('Successfully validated environment file')
+        return True
+    else:
+        raise exceptions.RegisterOrUpdateError(
+            'Exception validating environment file: {}'.format(
+                payload['message'])
+        )
+
+
 def register_or_update(clients, **workflow_input):
     """Node Registration or Update