Add a shutdown call to the wrapped XMPP socket

Per pull review suggestion

https://github.com/armooo/cloudprint/pull/63#discussion_r8629382
Small correction to cli help

The -c option was missing from the list.
Add option for more verbose logging

by setting the logging level to DEBUG.

Per suggestion on pull:
https://github.com/armooo/cloudprint/pull/63#discussion_r8629305
fuxup debug logging command line option