Eliminate "Node ping apparently hung" errors

The error was being triggered by logic to collect accounting
information starting and not being completed when testing to
start a node ping RPC. In other words, the logic wasn't testing
for the completion of one RPC against the start of that same
RPC, but against the start of a different RPC. This change
moves all of the timeout logic into the ping_nodes.c module
where we can make sure that the timing of different RPCs do
not get confused with each other.
bug 1190