fix call to list_routers()

Previously, we tried doing list_routers(router_id=blah), which
would result in novaclient always returning every router, with
no filtering.  Fix that so we only get the router we're looking
for.
"True" signifies that you want to list "all routers".  Now that I think about it, that might not be necessary for this case, but I don't remember what credentials the rug uses.  If the rug's user owns the routers, we can change that.