Currently DNS resolution is done automatically as part
of the creation of a QIOChannelSocket object instance.
This works ok for network clients where you just end
up a single network socket, but for servers, the results
of DNS resolution may require creation of multiple
sockets.

Introducing a DNS resolver API allows DNS resolution
to be separated from the socket object creation. This
will make it practical to create multiple QIOChannelSocket
instances for servers.
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>