relaxing validation of passed keys: 

by allowing a key options to be passed in it's now possible to specify cluster-wide variables

For example this control file would now work: 
```
(defcluster :int
  :options {
      :clj_fe_zk_root "clj-fe-zk-int"
      :clj-fe-zk-conn-str "10.251.76.40:2181,10.251.76.52:2181"}
  :clients [
    {:host "10.251.76.72" :user "root"}])

(defcluster :prod  
  :options {
      :clj_fe_zk_root "clj-fe-zk-prod"
      :clj-fe-zk-conn-str "10.250.76.63:2181,10.250.76.118:2181,10.250.76.119:2181"}
  :clients [
    {:host "10.250.76.180" :user "root" }])

(deftask :print-zk-options "printouts zk options for cluster" []
  (println (-> cluster :options :clj_fe_zk_root))
  (println (-> cluster :options :clj-fe-zk-conn-str)))
```