This will limit useless reloads (and related killSources), for instance
when transcoding parameters change. Also, improve the icecast
config generation test.

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.