Support for haproxy server options

This commit adds support for add additional backend server line
parameters that can control the behavior of haproxy.

It is intended to be able to apply the backup configuration flag
to the server lines in order to lock traffic to a single backend
server which is required for mysql.

Change-Id: I5af70abb96021146c098f788db349808d806a348
Merge "Support for haproxy server options"