Mark tripleo deploy experimental

The tripleo deploy command is experimental when not being invoked via
the containerized undercloud installation.

Change-Id: Ibd234c1232989921d13a9f5951797d0a66db5f93
Related-Blueprint: all-in-one

releasenotes/notes/tripleo-deploy-experimental-7533f9a9ed18a72d.yaml

@@ -0,0 +1,5 @@
+---
+features:
+  - |
+    [EXPERIMENTAL] The `openstack tripleo deploy` command is experimental
+    and may change in future releases.

tripleoclient/v1/tripleo_deploy.py

@@ -874,6 +874,13 @@ class Deploy(command.Command):
         return target
 
     def _standalone_deploy(self, parsed_args):
+        # NOTE(aschultz): the tripleo deploy interface is experimental but only
+        # when not being invoked via undercloud install. Print a warning...
+        if parsed_args.standalone_role != 'Undercloud' and \
+                parsed_args.stack != 'undercloud':
+            self.log.warning('[EXPERIMENTAL] The tripleo deploy interface is '
+                             'an experimental interface. It may change in the '
+                             'next release.')
         if not parsed_args.local_ip:
             msg = _('Please set --local-ip to the correct '
                     'ipaddress/cidr for this machine.')