Be more efficient about Foreman API calls

[sadsfae]

Clean up places where we're relying on hammer CLI calls per-host to query host parameters when we can do the work up front and query it cached in some other form or in general be more sparing about unnecessarily querying host parameters.

Example:

We can cut down on the number of needed Foreman calls substantially by removing the host list outside of the scope of the for loop here:

https://github.com/redhat-performance/quads/blob/master/bin/make-instackenv-json.sh#L51

In it's current implementation we're seeing way too many API calls in Foreman /var/log/production.log e.g.

2017-03-27 10:09:29 [app] [I]   Parameters: {"search"=>"params.nullos=false", "page"=>"1", "per_page"=>"1000", "apiv"=>"v2", :host=>{}}
2017-03-27 10:09:29 [app] [I] Authorized user admin(Admin User)
2017-03-27 10:09:30 [app] [I]   Rendered api/v2/hosts/index.json.rabl within api/v2/layouts/index_layout (768.6ms)
2017-03-27 10:09:30 [app] [I] Completed 200 OK in 998ms (Views: 743.7ms | ActiveRecord: 110.2ms

cat /var/log/foreman/production.log | grep "params.nullos=false" | wc -l
4922

[sadsfae]

Related - https://review.gerrithub.io/#/c/354578/