Add IPv6 http(s) health checking to ldirectord

When using IPv6 real servers, ldirectord does not support HTTP(S) health checks.
This patch adds a service type 'http' and 'https' with IPv6 real servers.

About workaround for Net-HTTP IPv6 Address URLs Broken,
See also: https://rt.cpan.org/Public/Bug/Display.html?id=75618
Merge pull request #379 from MichiroHibari/master

Medium: ldirectord: Add IPv6 http(s) health checking to ldirectord