implements blueprint multi-vendor-support-for-lbaas-step1
This patch implements the following changes:
* merge lbaas_plugin.py and plugin.py into 'plugin.py'
After that the default 'reference' implementation is available again.
* move all code related to reference implementation from plugin.py to
drivers/haproxy/plugin_driver.py
* Inherit HaproxyOnHostPluginDriver from abstract driver and implement
its interface.
* modify tests accordingly
Change-Id: Ib4bfe286826acdedeadbeeff4713448c073378d2
7176de17bd