Fix iptables rules when metadata_host=127.0.0.1

When metadata_host is set to 127.0.0.1 metdata_forward will use the
REDIRECT target instead of the DNAT target in iptables rules. The
REDIRECT target results in an implicit DNAT to the primary address
of the incoming interface. As a result requests coming in from VMs
will have a destination address of the gateway brought up by
nova-network.

metadate_accept will now allow traffic destinatined for any local
address on the metadata_port when metadata_host is set to
127.0.0.1.

Change-Id: I877befe6f7c1020d2160194b6f6cab8297cb086c
Fixes: bug #1202356
Merge "Fix iptables rules when metadata_host=127.0.0.1"