pam_usb: Shell injection via device UUID and username in pamusb-conf and pamusb-agent

pam_usb provides hardware authentication for Linux using ordinary removable media. Prior to 0.8.7, a crafted UUID such as $(id>/tmp/rce) in the config causes root RCE when pamusb-conf --reset-pads is run. A USB device with a crafted filesystem UUID (some controllers allow this) can inject the payload at --add-device time. Also, userName from the XML config is passed to os.system() in pamusb-agent, which invokes a shell. This vulnerability is fixed in 0.8.7.