Fix #270 - uri-for-entity-type to allow multiple uri's for the same type.  Which one is returned depends on what vars are bound.  If none of the requirements are met, it will print out all the possibilities in the exception.

katello.api-tasks> (binding [katello.conf/*session-org* "ACME_Corporation" *env-id* 1] (uri-for-entity-type :repository))
"api/organizations/ACME_Corporation/environments/1/repositories"
katello.api-tasks> (binding [katello.conf/*session-org* "ACME_Corporation" *product-id* 1] (uri-for-entity-type :repository))
"/api/organizations/ACME_Corporation/products/1/repositories"