Update tests in test_map_legend.

* Update the test to use tests data from source tree (test_add_class_to_legend, test_add_symbol_to_legend, test_get_legend, test_get_raster_legend, test_get_vector_legend)
* Add 1 raster impact layer (we haven't had impact layer test data that is a raster)
* Update some control images

Signed-off-by: Akbar Gumbira <akbargumbira@gmail.com>