Wait for IOM to come back online after restart instead of fixed sleep

A fixed 30s sleep is not enough for a full BMC boot cycle. Add
_wait_for_iom_online() which polls GET /redfish/v1/ every 15s until the
IOM responds (up to 5 minutes), then call it after every IOM restart in
both _update_iom_fw and _update_fabric_fw. This ensures the fabric card
update (and post-update validation) don't run while the IOM is still
booting and unreachable.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

modules/redfish.py

@@ -181,6 +181,25 @@ def _redfish_poll_tasks(password: str, host: str, timeout: int = 600) -> tuple:
     return False, f"Timeout after {timeout}s waiting for tasks."
 
 
+def _wait_for_iom_online(password: str, host: str, timeout: int = 300) -> bool:
+    """
+    Poll GET /redfish/v1/ until the IOM responds successfully, indicating it
+    has finished rebooting.  Waits up to `timeout` seconds.
+    Returns True if the IOM came back online, False if timeout was exceeded.
+    """
+    deadline = time.monotonic() + timeout
+    attempt  = 0
+    while time.monotonic() < deadline:
+        attempt += 1
+        ok_flag, _ = _redfish_request(password, "GET", "/redfish/v1/", host=host)
+        if ok_flag:
+            return True
+        elapsed = int(time.monotonic() - (deadline - timeout))
+        info(f"  Waiting for IOM to come back online... [{elapsed}s elapsed]")
+        time.sleep(15)
+    return False
+
+
 def _redfish_restart_iom(password: str, host: str, iom: str) -> tuple:
     return _redfish_request(
         password, "POST",