python3: Fix traceback while running tests

Fix:

TypeError: Unicode-objects must be encoded before hashing

while running tests. This is due to the fact in python3 hashlib.md5
works with bytes and we are passing unicode strings.

Change-Id: I27a57d6afb2412e11bc2802e4559d56c5b5592a9
Signed-off-by: Chuck Short <chuck.short@canonical.com>