DNS health check.

1. Add a package for http://www.dnspython.org/
2. Add dnsck, a utility using dnspython.org to check
   for responses from DNS servers.
3. Make psstat run dnsck in its network test loop.
4. Also fix find-servers in psstat for platforms which
   do not have find-servers installed.

Change-Id: I4051269d7a7b7e63a8390026c3b8d6de5d5ab4ec
9 files changed