sunet-fleetlock: handle connection errors

In order to handle upgrades of the fleetlock server when running only
one server we need to handle connection errors like connection refused
or timed out errors gracefully.

Because there are several different ways the connection can fail and it
is hard to keep track of them all, just catch everything. We then also
need special handling of our own timeout execption so we are not
accidentally stuck retrying forever.

Also fix so we actually use the request_timeout arg for individual HTTP
requests instead of the global timeout.

While here run isort to keep imports tidy.

global/overlay/usr/local/bin/sunet-fleetlock

@@ -24,20 +24,21 @@
 # When modifying this code please make sure it is passed through the following
 # tools:
 # ===
+# isort
 # black
 # pylint
 # mypy --strict
 # ===
 
-import platform
-import sys
-import signal
-import time
 import argparse
 import configparser
 import os.path
-from typing import Optional, Union
+import platform
+import signal
+import sys
+import time
 from types import FrameType
+from typing import Optional, Union
 
 import requests
 
@@ -80,19 +81,29 @@ def do_fleetlock_request(
     request_id_key = "request-id"
     request_id = None
 
+    retry_sleep_delay = 1
+
     # Loop forever: we depend on the SIGALRM timout to raise an error if it
     # takes too long
     while True:
         if args.verbose:
             print(f"{operation} POST at url {url}")
 
+        try:
             resp = requests.post(
                 url,
                 headers=fleetlock_headers,
                 json=fleetlock_data,
-            timeout=args.timeout,
+                timeout=args.request_timeout,
                 auth=("", config[args.lock_group]["password"]),
             )
+        except Exception as e:  # pylint: disable=broad-exception-caught
+            if isinstance(e, TimeoutException):
+                # This means our global timer is up, no more time to retry
+                raise e
+            print(f"POST request failed: {e}")
+            time.sleep(retry_sleep_delay)
+            continue
 
         if request_id_key in resp.headers:
             request_id = resp.headers[request_id_key]
@@ -126,7 +137,7 @@ def do_fleetlock_request(
             + f"({request_id_key}: {request_id})"
         )
 
-        time.sleep(1)
+        time.sleep(retry_sleep_delay)
 
 
 def read_config(args: argparse.Namespace) -> Union[configparser.ConfigParser, None]: