Add method to compute Imgae Store capacity from global setting

Author: Dingane Hlaluku

server/src/main/java/com/cloud/server/StatsCollector.java

@@ -1364,6 +1364,14 @@ public boolean imageStoreHasEnoughCapacity(DataStore imageStore) {
         return false;
     }
 
+    public boolean imageStoreHasEnoughCapacity(DataStore imageStore, Double storeCapThreshold) {
+        StorageStats imageStoreStats = _storageStats.get(imageStore.getId());
+        if (imageStoreStats != null && (imageStoreStats.getByteUsed() / (imageStoreStats.getCapacityBytes() * 1.0)) <= storeCapThreshold) {
+            return true;
+        }
+        return false;
+    }
+
     /**
      * Sends VMs metrics to the configured graphite host.
      */