Warn / log if DNS TTL is long/infinite

[willholley]

When debugging connection issues, it would be useful to know the DNS caching policy. Perhaps we could log the value of java.security.Security.getProperty("networkaddress.cache.ttl"); when the library is initialised?

[ricellis]

One thing to consider is that calling Security.getProperty is itself restricted by a SecurityPermission. [1]

So in the case where a SecurityManager is active (the most likely scenario for an infinitely cached DNS entry) we may not have access to read the value anyway and would need to handle the security exception.