Update proxy.conf example with the latest pipeline

On the section Install and configure the proxy
node, step 4, the proxy.conf is not using the
latest pipeline

It's missing couple of pipelines which are
essential (e.g proxy-logging should
be twice, gatekeeper)

Added the pipeline catch_errors which
handles error and sets a transaction id
for every request

Added gatekeeper to remove private request
and headers which client should not
generate

Added proxy-logging which logs request
made to proxy server (e.g. PUT,GET)

Second proxy-logging pipeline is for
middleware the can return custom response

The pipelines are referenced from swift git
repo's proxy.conf-sample file

Retains the existing authtoken keystoneauth
middleware section

Closes-Bug: 1322126

Change-Id: Iee005b0117ac452c724bc40f1393e97fe66ee8c1
Merge "Update proxy.conf example with the latest pipeline"