If an image has been tagged to multiple repos and tags, 'docker
rmi -f IMAGE_ID' will just untag one random repo instead of
untagging all and deleting the image. This patch implement
this. This commit is composed of:
*untag all names and delete the image
*add test to this feature
*modify commandline/cli.md to explain this
Signed-off-by: Deng Guangxing <dengguangxing@huawei.com>