update docstring for conf class

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
improve get_list to actually return lists

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
adds a bunch of tests for the new get_list helper

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>