[BB200] Restore locking mechanism to update IMEX nodes config.

Even if now the config file is local and we assume exclusive job allocation,
having the locking mechanism prevents impacts on IMEX when concurrent jobs are submitted.

Author: gmarciani

tests/integration-tests/tests/ultraserver/test_gb200/test_gb200/91_nvidia_imex_prolog.sh

@@ -91,9 +91,40 @@ function write_file() {
     return 1 # Not Updated
   fi
 
-  echo "${_content}" > "${_file}"
-  info "File ${_file} updated"
-  return 0 # Updated
+  # Try to acquire lock with timeout
+  (
+      if ! flock -x -w ${_lock_timeout_seconds} 200; then
+        # If timeout, assume deadlock and try to recover
+        info "Lock timeout after ${_lock_timeout_seconds}s, attempting deadlock recovery"
+        exit 1
+      fi
+      echo "${_content}" > "${_file}"
+  ) 200>"${_lock_file}"
+
+  local _lock_result=$?
+
+  if [[ ${_lock_result} -eq 0 ]]; then
+    return 0 # Updated successfully
+  fi
+
+  # Deadlock recovery: remove stale lock file and retry once
+  error "Potential deadlock detected for ${_file}, attempting recovery"
+  rm -f "${_lock_file}"
+  sleep 1  # Brief pause to avoid race conditions
+
+  (
+      if ! flock -x -w 10 200; then
+        exit 1
+      fi
+      echo "${_content}" > "${_file}"
+  ) 200>"${_lock_file}"
+
+  if [[ $? -eq 0 ]]; then
+    info "Lock acquired after deadlock recovery for ${_file}"
+    return 0 # Updated
+  fi
+
+  error_exit "Failed to acquire lock for ${_file} even after deadlock recovery"
 }
 
 function reload_imex() {