support multiple sets of airship files

To support multiple site types that may require different
airship-treasuremap files and site templates, the yaml
build tools will now use the variables AIRSHIP_TREASUREMAP
and AIRSHIP_TEMPLATES to locate the files needed.  These
variables are set in the set_site_env.j2 templates
based on the site_type defined in the input yaml file.

Change-Id: Ie3dcf5f8ebbc4ce57bce1cb89dc8fc53ce77776d
Signed-off-by: davidplunkett <dp7642@att.com>