[COOK-2384] Add haproxy LWRP for multiple haproxy sites/configs

https://tickets.opscode.com/browse/COOK-2384

Create a lwrp to manage basic configuration blocks such as listen, frontend and backend.
This allow to manage easily (without modifying the template) a broader spectrum of haproxy conf.
Example of uses are set in readme file.

LWRP only sets attributes which allow to configure directly via attributes (in a role for instance) or with lmrp for complex  (involving search for instance) setups.