Fix traceback in Alerts when inserting USB drive

I plugged a usb drive into the M50 HA system, running rueNAS-11.2-MASTER-201904220659,  and got the following alert in the GUI:

CRITICAL: April 25, 2019, 1:29 p.m. - Standby Controller - Unable to run alert source 'USBStorage' Traceback (most recent call last): File "/usr/local/lib/python3.6/site-packages/middlewared/plugins/alert.py", line 431, in _run_source alerts = (await alert_source.check()) or [] File "/usr/local/lib/python3.6/site-packages/middlewared/alert/base.py", line 96, in check return await self.middleware.run_in_thread(self.check_sync) File "/usr/local/lib/python3.6/site-packages/middlewared/main.py", line 1005, in run_in_thread return await self.loop.run_in_executor(executor, functools.partial(method, *args, **kwargs)) File "/usr/local/lib/python3.6/concurrent/futures/thread.py", line 56, in run result = self.fn(*self.args, **self.kwargs) File "/usr/local/lib/middlewared_truenas/alert/source/usb_storage.py", line 23, in check_sync title=[usbdevname], TypeError: __init_() got multiple values for argument 'title'