SPEC: add some well-known error codes
SPEC: add some well-known error codes

Signed-off-by: Bruce Ma <f8b1e5646bfe3ba4fa1f3474ce1ccbc1bbf22133@gmail.com>

dcbw/cni,containernetworking/cni,appc/cni,containernetworking/cni,appc/cni,dcbw/cni