launch: add a probe for ssh after reboot

We do more operations after rebooting the host (getting ssh keys,
etc.).  Put in a small loop to wait for it to reappear.

Change-Id: Ibfaf530bba8f84bc5a6110e3dd7e7c73be7d5f4f

launch/src/opendev_launch/launch_node.py

@@ -21,6 +21,7 @@
 import argparse
 import os
 import shutil
+import socket
 import subprocess
 import sys
 import threading
@@ -228,6 +229,19 @@ def bootstrap_server(server, key, name, volume_device, keep,
         else:
             raise
 
+    timeout = 120
+    start = time.perf_counter()
+    while True:
+        try:
+            print("Waiting for ssh...")
+            with socket.create_connection((host_ip, 22), timeout=5):
+                break
+        except OSError as e:
+            if time.perf_counter() - start >= timeout:
+                raise Exception("Host did not reboot within timeout")
+            time.sleep(10)
+            print("Host rebooted!")
+
 
 def build_server(cloud, name, image, flavor,
                  volume, keep, network, boot_from_volume, config_drive,