When g_option_context_parse fails, context and error variables are not getting free'd
which results in memory leaks. Free'ing the same.
And replacing g_error_free with g_clear_error, which checks if the error being passed
is not NULL and sets the variable to NULL on free'ing.
https://bugzilla.gnome.org/show_bug.cgi?id=753852
Just shows devices with basic info and exits. Or will
wait for more devices to show up or be removed with
the --follow option. It's also possible to pass filters
as command line arguments in the form DEVICE_CLASSES
or DEVICE_CLASSES:CAPS.
