Previously they were testing many things which were not configuration.
All we care about is whether settings are read/writeable via the methods
provided.

This requires a parameter to be accepted by the block passed to
Geocoder.configure, which means you don't need to remember that the
method is called "config"--you can call it whatever you want.
This behavior seems more standard for configuration blocks.

It's not an ideal name either, but it's short and it's slightly more
specific than "method".

Removed set_defaults from all tests and replaced with teardown to reset the defaults.

Signed-off-by: James McCarthy <james2mccarthy@gmail.com>