Adds a new metric to NodeStatus (MaxListeners) so that it is available
to the traffic control logic.

Increase robustness of the config watcher by reloading the full
configuration on Etcd errors (fixes an issue with the very common error
401).

Make sure that the Icecast config reload is only triggered if the
configuration has actually changed.

Added a way to stop the node properly, which ensures that we are
tracking all the resources and that there are no deadlocks in the
internal communications.

MasterElection now closes the update channel when it's done.

Master election code should be more robust now, this commit eliminates
the discrepancy between role and master info (previously it was possible
for these two to be non synchronized).

This commit also includes an in-memory etcd mock, which implements
enough of the etcd interface to test the masterelection code.

Introduce node names, allowing a node to have multiple IP addresses.
Also, make the front-end code IPv6-aware and support AAAA records.

This is an attempt to fix a problem where sources would become stuck
on master -> slave state transitions.

This allows running the service on a single port: with the
--enable-icecast-proxy option, all requests can go through
redirectord.

Make progress anyway when the history is gone.

go-etcd now closes the channel passed to Watch() on error, so we need
to restart the syncer every time and use a temp channel.