update CHANGELOG.MD

Signed-off-by: Liu Yuan <namei.unix@gmail.com>
dog: show actual redundancy scheme for 'vdi list'

With this patch, 'vdi list' will show actual redundancy as follow:

yliu@ubuntu-precise:~/sheepdog$ dog/dog vdi list
  Name        Id    Size    Used  Shared    Creation time   VDI id  Copies  Tag
  test         0   10 MB  0.0 MB  0.0 MB 2014-01-21 15:54   7c2b25    4:2              
  test1        0   20 MB  0.0 MB  0.0 MB 2014-01-21 15:59   fd32fc      3 

Signed-off-by: Liu Yuan <namei.unix@gmail.com>