dog/node: add raw output support for dog node md info

As titled. A command line crash as below is also fixed.

$ dog node md plug -A
dog exits unexpectedly (Segmentation fault).
dog() [0x405dda]
/lib/x86_64-linux-gnu/libpthread.so.0(+0xfbaf) [0x7fd6003c9baf]
dog() [0x40d8b2]
dog() [0x40706e]
dog() [0x40398c]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf4) [0x7fd600013de4]
dog() [0x403cea]
Segmentation fault

Signed-off-by: Ruoyu <liangry@ucweb.com>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>
dog: forbid creating snapshot of hypervolume

Currently it is not supported.

Cc: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Cc: Valerio Pachera <sirio81@gmail.com>
Cc: Alessandro Bolgia <alessandro@extensys.it>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>
dog: use nr_copies of inode object instead of command line parameter

Current "dog vdi clone" has a possibility of creating clone volume
which has a different replica number from its original volume when it
receives -c option. This patch forbid such a situation by letting
vdi_clone() use inode->nr_copies instead of vdi_cmd_data.nr_copies
(the variable which holds a value passed with -c option).

Cc: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Cc: Valerio Pachera <sirio81@gmail.com>
Cc: Alessandro Bolgia <alessandro@extensys.it>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>