Change cms_sign_data to use sha256 message digest
Change cms_sign_data to use sha256 message digest

cms_sign_data was not passing the md parameter to openssl, so it was
using the default digest of sha1. Some security standards require a
SHA2 algorithm for the digest.

This if for security hardening.

SecurityImpact

Change-Id: Iff063149e1f12df69bbf9015222d09d798980872
Closes-Bug: #1362343

ging/python-keystoneclient,klmitch/python-keystoneclient,magic0704/python-keystoneclient,magic0704/python-keystoneclient,darren-wang/ksc,ging/python-keystoneclient,alexpilotti/python-keystoneclient,klmitch/python-keystoneclient,Mercador/python-keystoneclient,sdpp/python-keystoneclient,darren-wang/ksc,sdpp/python-keystoneclient,Mercador/python-keystoneclient,alexpilotti/python-keystoneclient