Use ingress.appscode.com/keep-source-ip: true to preserve source IP

[tamalsaha]

This preserves source IP for LoadBalancer type ingresses for aws, gce, gke, azure. The actual configuration generated depends on the underlying cloud provider.

• gce, gke, azure: Adds annotation service.beta.kubernetes.io/external-traffic: OnlyLocal
  to services used to expose HAProxy.
  ref: https://kubernetes.io/docs/tutorials/services/source-ip/#source-ip-for-services-with-typeloadbalancer

• aws: Enforces the use of the PROXY protocol over any connection accepted by any of
  the sockets declared on the same line. Versions 1 and 2 of the PROXY protocol
  are supported and correctly detected. The PROXY protocol dictates the layer
  3/4 addresses of the incoming connection to be used everywhere an address is
  used, with the only exception of "tcp-request connection" rules which will
  only see the real connection address. Logs will reflect the addresses
  indicated in the protocol, unless it is violated, in which case the real
  address will still be used. This keyword combined with support from external
  components can be used as an efficient and reliable alternative to the
  X-Forwarded-For mechanism which is not always reliable and not even always
  usable. See also "tcp-request connection expect-proxy" for a finer-grained
  setting of which client is allowed to use the protocol.
  ref: https:/kubernetes/kubernetes/blob/release-1.5/pkg/cloudprovider/providers/aws/aws.go#L79 (this was implemented in Add annotation to add accept-proxy in bind statements #144)

Fixes #146, #100