make scheduling evenly distribute slots across all hosts

[lyogavin]

#359

Changed the way even schedule distribute slots into also considering the number of used slots across all hosts. Make sure the new assignment use slots evenly across all hosts.

[xiaokang]

Just change sort-slots works on out cluster. The code is bellow:

Index: src/clj/backtype/storm/scheduler/EvenScheduler.clj
===================================================================
--- src/clj/backtype/storm/scheduler/EvenScheduler.clj
+++ src/clj/backtype/storm/scheduler/EvenScheduler.clj
@@ -7,7 +7,12 @@
 :implements [backtype.storm.scheduler.IScheduler]))

 (defn sort-slots [all-slots]
-  (let [split-up (vals (group-by first all-slots))]
+  (let [split-up 
+         (map second 
+           (reverse 
+             (sort 
+               (for [[host ports] (group-by first all-slots)] 
+                 [(count ports) ports]))))]
     (apply interleave-all split-up)
     ))