Add openstack/common/crypto from OSLO

Add cinder/openstack/common/crypto/__init__.py and
cinder/openstack/common/crypto/utils.py.

They are needed in cinder/openstack/common/rpc/securemessage,
which is updated in the following commits.

Oslo version: 4987d09a28c986bdca0921a1d0f062ac9328904f

Change-Id: I15e7ce3b84831fd247ea155a3b15829348087830
Merge "Add openstack/common/crypto from OSLO"