Refactor the way client is initialized. We need to ensure that
clients are not added to the clients map and readLoop started if
the server is in the process of being shutdown otherwise there
is a chance that the server already gathered the list of connections
to close and this one would not be included, leaving a readLoop
running.
Same occurs for routes, with the complexity that the readLoop is
started well before the route connection is added to the server
routes' list. We need a temporary map that contains those connections
to be able to close them on server Shutdown.
Fixed some flapping tests.
Both seed and chained cases are now handled properly when servers
connect quickly and concurrently to one another.
When accepting a route, the server will forward the new route INFO
protocol to its known routes. In turn those routes will connect
to the new server (if not already connected).
A retry for implicit route was introduced to mitigate the issue
with two servers connecting to each other and electing the opposite
connection as the winner, resulting in both connections being dropped.
The server with smaller ID will try once to reconnect.
Some tests were fixed to handle possible extra INFO protocol.
New tests added.
Fix issue: https://github.com/nats-io/gnatsd/issues/206
