This patch enables the configuration of the extended resolver's time out for the dns lookup.
A new configuration parameter solr.resolver.timeout (sorry for yet another config param) is introduced and used to set the timout in DnsLookup.java.
For backward compatibility the time out defaults to 20 milliseconds.
OS time outs vary between 2 to 5 seconds, from what I've learned so far.
We did face an increasing number of solr errors (200- 900/day) due to timeout, with the timeout being set to 20 milliseconds. Setting it to the system defaults (5 seconds) got rid of most of these. Nowadays an average of 2/day do occur.