In 4f6ca43e1f we started to use
the bytearray type as 'b' type, but PyCrypto insists on getting
a bytes type.
This fixes the following Exception:
TypeError: argument 1 must be read-only bytes-like object, not bytearray
Change-Id: If2a727ed417ffd56c0f7d7b4e9f633d67fde5ced
Closes: OS#5060