test: ssh: Wait for target SSH server to launch, by default

By default, ensure that the target device accepts TCP connections on
the specified port before returning the device object. This aligns the
SSH implementation with {NET,REST}CONF.

This solves the issue where tests that use SSH commands early in their
execution would sometimes fail as the remote server had not started up
yet.

Author: wkz

test/infamy/ssh.py

@@ -1,7 +1,7 @@
 import subprocess
 
 from dataclasses import dataclass
-from . import env
+from . import env, netutil, util
 
 
 @dataclass
@@ -15,6 +15,9 @@ class Location:
 import subprocess
 import os
 
+def ssh_syn(addr, port=22):
+    return netutil.tcp_port_is_open(addr, port)
+
 def fetch_file(remote_user, remote_address, remote_file, local_file, key_file, check=False, remove=False):
     """
     Fetches a file over SSH using scp and the provided private key.
@@ -62,9 +65,12 @@ def fetch_file(remote_user, remote_address, remote_file, local_file, key_file, c
             print(f"Error removing fetched file {local_file}: {e}")
 
 class Device(object):
-    def __init__(self, name: str, location: Location):
+    def __init__(self, name: str, location: Location, wait: bool=True):
         self.name = name
         self.location = location
+        if wait:
+            util.until(lambda: ssh_syn(location.host, location.port))
+
     def __str__(self):
         nm = f"{self.name}"
         if env.ENV.ltop: