NodeDiscovery threads have non-unique name

[quidryan]

There is no thread name format provided to the ThreadFactoryBuilder, so they get the hard-to-understand name pool-5-thread-1.

https://github.com/Netflix/astyanax/blob/master/astyanax-core/src/main/java/com/netflix/astyanax/connectionpool/impl/NodeDiscoveryImpl.java#L62

Adding a .setNameFormat("AstyanaxNodeDiscovery-%d") should fix it.