Cfy 1272 allow any distribution when installing agents

- removed specific distribution forcing.
- added ability to specify any known agent resource in blueprint under cloudify_config
- supplied download_resource_on_host and get_resource_origin_url functions.
- download_resource_on_host will attempt to use either wget or curl.
cant happen...the get_agent_resource_url will never return None.

You can add this validation inside the method, to avoid duplication further down