(#20194) Do not perform reverse DNS lookups in webrick

Previously, the webrick-based puppet master would perform a reverse DNS lookup on
every connected socket, even authenticated connections. This occurs when
puppet calls IPSocket#peeraddr to get its peer's IP address. But ruby
would by default perform a reverse lookup at the same time.

This commit sets the global setting via
BasicSocket.do_not_reverse_lookup to handle ruby 1.8.x and up.

The commit also sets the webrick :DoNotReverseLookup configuration
option, which is necessary on at least 1.9.2p0.

Paired-with: Andy Parker <andy@puppetlabs.com>