Python 3: fix the _calc_signature_* functions

This commit makes the _calc_signature_* functions work in python 3. The issues
were usual text strings vs bytes that arise when porting code to Python 3.

Change-Id: I36b40012b09d4f72e9248b49d51dc545d70abfc6
Merge "Python 3: fix the _calc_signature_* functions"