CLOUDSTACK-1302: Make sure the disk cache mode is passed to the KVM Agent

The StartCommand did not contain the proper cache mode due to VolumeJoinVO
not containing the cache_mode field.

server/src/com/cloud/api/query/vo/VolumeJoinVO.java

@@ -201,6 +201,9 @@ public class VolumeJoinVO extends BaseViewVO implements ControlledViewEntity {
     @Column(name = "iops_write_rate")
     Long iopsWriteRate;
 
+    @Column(name = "cache_mode")
+    String cacheMode;
+
     @Column(name = "pool_id")
     private long poolId;
 
@@ -492,6 +495,10 @@ public class VolumeJoinVO extends BaseViewVO implements ControlledViewEntity {
         return iopsWriteRate;
     }
 
+    public String getCacheMode() {
+        return cacheMode;
+    }
+
     public long getPoolId() {
         return poolId;
     }