When HAProxy is run in multi-process mode, the single stats page
shows metrics for one of the processes at a time, with a random
selection made on page reload.
Whilst a more complete solution may be to enable a stats page for
each process, this is a little cumbersome. This addition allows
the stats page to be pinned to one process, providing a partial
snapshot of the state of the instance.
Change-Id: Id9314e5b267aafeaf34c82874eb8bfe0713dfac3