Use bytes to accommodate python3
Use bytes to accommodate python3

python3 will not convert bytes to string implicitly. Concatenate bytes
with string will report error in python3. Just use bytes in the case.

Change-Id: Ibbec76b726a3f5fef84a4c7cf93b3c065614e133

openstack/dragonflow,openstack/dragonflow,openstack/dragonflow