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>