Use HAProxy 1.5.1, the latest released version.
Use rs-haproxy/source/url to determine the version of HAProxy being installed.
Raise if unable to detemine haproxy version from source filename.
Cosmetic change in raise comment.
Create and use helper to obtain haproxy version from source URL.
Merge pull request #15 from rightscale-cookbooks/white_14_08_acu173777_use_haproxy_15_ga

White 14 08 acu173777 use haproxy 15 ga