uses os.urandom instead of Crypto.Random for backward compatibility

Crypto.Random has been introduced by pycrypto 2.1 but in RHEL6 and
derivates you will only find pycrypto 2.0.1

Change-Id: Ib601981b0b8fcb5b3e8fc8761ee05adf7f6574fa
Merge "uses os.urandom instead of Crypto.Random for backward compatibility"