Add date as version under /etc/version when build vyos image
Add date as version under /etc/version when build vyos image

for https://github.com/zxwing/premium/issues/1402

Signed-off-by: Mei Lei <d1c6e4e75080176552ef8271b379adabccaa7551@gmail.com>

zstackorg/zstack-vyos,zstackorg/zstack-vyos,zstackorg/zstack-vyos