Support standalone services

* Do not include main plugin in server recipe and
everywhere else, so that we can manage services
with roles on independent servers
* Support an independent quantum api server not running
any of the agents or packages required by plugin
* Fix ordering issues with openvswitch-agent install.
* Try to unify platform_options names across
distributions.
* Introduce a common.rb for setting up templates
required by nearly everything, like quantum.conf.
* Plugin recipes now serve to only install any
additional components required

Change-Id: Ieb7c357baf882c9078dbdd577f53448af863c931