ab: try all destination socket addresses returned by apr_sockaddr_info_get
instead of failing on first one when not available.
Needed for instance if localhost resolves to both ::1 and 127.0.0.1
e.g. if both are in /etc/hosts.

ab: Use only one connection to determine working destination socket address.

Submitted by: rjung
Reviewed by: rjung, covener, ylavic


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1826891 13f79535-47bb-0310-9956-ffa450edef68