fix(cleanup): properly handle FileSR exception for slave check

A plugin is used by the `_checkSlave` helper.
Therefore, `call_plugin` is executed instead of a command helper, which means that `CommandException` cannot be raised.

Signed-off-by: Arnaud Garcia-Fernandez <arnaud.garcia-fernandez@vates.tech>

Author: Ythogtha

drivers/cleanup.py

@@ -3000,7 +3000,7 @@ def _checkSlaves(self, vdi):
                 raise AbortException("Aborting due to signal")
             try:
                 self._checkSlave(hostRef, vdi)
-            except util.CommandException:
+            except XenAPI.Failure:
                 if hostRef in onlineHosts:
                     raise