Python 3: make tests from v2_0/test_access.py pass

This fixes calls to the hash_signed_token() and cms_hash_token() functions, by
making sure they are given bytes.

Change-Id: I83ac48a845cd09150b01afad6f0549ee83c20ddd
Merge "Python 3: make tests from v2_0/test_access.py pass"