Add Support for Splitting Proxy and Storage Networks

Previously, both proxy and storage (ring) interfaces utilized
the same IP address.  This is an uncommon deployment model,
as proxy and storage/ring services are usually seperated across
multiple networks.

This change introduces the new parameter swift_proxy_net_ip that
alows users to specify a seperate ip address for binding the
Swift proxy service.  Defaults to the same address as the
swift_local_net_ip parameter ($::ipaddress_eth0) for backwards
compatibility and for proxy/storage networks to share the same ip

Change-Id: I2cc6bd9e430a93596236b2b5c8015cf32c981502
Merge "Add Support for Splitting Proxy and Storage Networks"