make to_list more forgiving
make vstruct(Peers) a proper generator
start_nodes should only be called with a list argument
voting.hrl: not needed
rafter_voting:member added
to_list: allow undefined as argument
stop nodes in Running list

.. rather than retrieving the list of running nodes from the state --
this is a workaround to make the test run, not sure if it's actually
valid.
"oneof" not needed, initialise with vstruct instead of list
hack: disable precondition
use rafter_voting:member
more general server/vstruct generation
start_nodes: accept vstruct too
initialise state with vstruct instead of list
make use of rafter_voting:member
Running is a vstruct now
more general vstruct generation