The code was written long ago, when the python3 bytearray type
probably didn't exist yet, or was at least not known. Let's stop
using string types with binary bytes inside, and instead standardize
on two types:
* bytearray for binary data
* string for hexadecimal nibbles representing that binary data
Change-Id: I8aca84b6280f9702b0e2aba2c9759b4f312ab6a9
4f6ca43e1f