Adding Login Scanner for MyBook Live

This is a LoginScanner auxiliary module for Western
Digital MyBook Live NAS devices as well as the spec
for testing.
How do these relate to what is done in ```set_sane_defaults```?  To me, it looks like the defaults are set in ```set_sane_defaults```, but ```attempt_login``` uses an explicit ```method``` and ```uri``` seemingly not derived from anything else, implying that there isn't an option exposed to try a different URI.  Huh?