dog: remove alter subcommand and migrate sub-sub commands

The name of subcommand "dog alter" is strange and confusing. Because
many other commands of dog alter state of sheep cluster. This patch
removes the subcommand and move sub-sub commands as below:
- dog alter vdi-copy -> dog vdi alter-copy
- dog alter cluster-copy -> dog cluster alter-copy

Reviewed-by: Ruoyu <liangry@ucweb.com>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>