fixes #6856 - API v2 - more efficient import puppetclasses for single environment

@eLobato, not following, you write that the both tests will fail?? Both of the tests I added passed, but there is an obscure failure for 1.8.7/mysql http://ci.theforeman.org/job/test_develop_pr_core/2532/database=mysql,puppet=3.0,ruby=1.8.7/
I'll squash and rebase.