Add check for disable_upgrade_deployment flag in roles_data

Check that the disable_upgrade_deployment flag is set in any
operator provided roles_data.yaml file (the --roles-file
parameter).

This is an alternative proposal to
I9327f42bfbebf050f79224ee1c1ff41e49b9c2fd and the advantage
here is that we can use the existing validation_warnings_fatal
to raise the exception or stay at logging a warning. The
validation_warnings_fatal defaults to False.

Related-Bug: 1699792
Change-Id: I606a3010e7ecd83f34b852a35ed298c30f65adeb

releasenotes/notes/add-check-for-disable-upgrade-deployment-flag-f074554e47e85b27.yaml

@@ -0,0 +1,8 @@
+---
+upgrade:
+  - If the operator specifies a roles_data.yaml for the deployment or upgrade
+    this adds a check that the disable_upgrade_deployment flag is set at least
+    once in that file and otherwise logs a warning. If the
+    validation-warnings-fatal parameter is set to True (default is False) then
+    this check will also raise an InvalidConfiguration exception.
+

tripleoclient/v1/overcloud_deploy.py

@@ -567,6 +567,25 @@ class DeployOvercloud(command.Command):
                     "Error: The following files were not found: {0}".format(
                         ", ".join(nonexisting_envs)))
 
+        # Check if disable_upgrade_deployment is set once
+        self.log.debug("Checking that the disable_upgrade_deployment flag "
+                       "is set at least once in the roles file")
+        if parsed_args.roles_file:
+            roles_data = yaml.safe_load(open(parsed_args.roles_file).read())
+            disable_upgrade_deployment_set = False
+            for r in roles_data:
+                if r.get("disable_upgrade_deployment"):
+                    disable_upgrade_deployment_set = True
+                    break
+            if not disable_upgrade_deployment_set:
+                self.log.warning(
+                    "The disable_upgrade_deployment flag is not set in the "
+                    "roles file. This flag is expected when you have a "
+                    "nova-compute or swift-storage role. Please check the "
+                    "contents of the roles file: %s" % roles_data)
+                if parsed_args.validation_warnings_fatal:
+                    raise exceptions.InvalidConfiguration()
+
     def _get_default_role_counts(self, parsed_args):
 
         if parsed_args.roles_file: