* request: in the event of failure, try other IPs (#6761)
In the case where a name has multiple A/AAAA records, we should
try subsequent records instead of immediately failing when we have a
failure on the first IP address.
This significantly improves delivery success when there are network
connectivity problems affecting only IPv4 or IPv6.
* fix method call style
* request_spec: adjust test case to use Addrinfo
* request: Request/open: move private addr check to within begin/rescue
* request_spec: add case to test failover, fix exception check
* Double Addrinfo.foreach so that it correctly yields instances
36b5703796