Add Happy-Eyeballs style IPv6 connection establishing.

Add Happy-Eyeballs style IPv6 connection establishing.

In the cases where a DNS lookup will give you both an IPv4 and IPv6
address, this will start two connection channels at the same time.
One trying to connect using IPv4 and one on IPv6. This is done so
that we can use the fastest one for the connection. To do this we
have to do the hostlookup in the connection. The result is then
in the cache for the individual socket so it will not need to do
another lookup.

Task-number: QTBUG-16458
Change-Id: I806c20168d9c5edc2831b80f82a2bd570b36d5fa
Reviewed-on: http://codereview.qt.nokia.com/1003
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Shane Kearns <shane.kearns@accenture.com>