unable to load certificate should abort request

If openssl returns with a command line error (3), we assume
the PKI certificate is not properly installed.  Added
'try ... except' blocks to cms_sign_text and cms_sign_token
calls.

Fixes: bug #1103569
Change-Id: Iad98738e990d3ab1ec0d0015840d76cf948ae560
Merge "unable to load certificate should abort request"