Don't use deprecated BaseException.message
Don't use deprecated BaseException.message

When running the unit tests, I'd get a warning message:

 /opt/stack/keystone/tests/test_exception.py:151: DeprecationWarning: BaseException.message has been deprecated as of Python 2.6

We shouldn't be using deprecated functions.

This change makes it so the test doesn't use the deprecated member.

Also, test_unicode_message wasn't a test for security error
formatting so moved it to ExceptionTestCase.

Change-Id: I088bf94433baf0f00d3ff8ca63e5f74e9d300cd0

blueboxgroup/keystone,reeshupatel/demo,dstanek/keystone,rushiagr/keystone,klmitch/keystone,UTSA-ICS/keystone-kerberos,rodrigods/keystone,ilay09/keystone,idjaw/keystone,rushiagr/keystone,MaheshIBM/keystone,citrix-openstack-build/keystone,dsiddharth/access-keys,dstanek/keystone,takeshineshiro/keystone,idjaw/keystone,derekchiang/keystone,vivekdhayaal/keystone,jumpstarter-io/keystone,rickerc/keystone_audit,mahak/keystone,roopali8/keystone,dims/keystone,townbull/keystone-dtrust,jamielennox/keystone,vivekdhayaal/keystone,rajalokan/keystone,himanshu-setia/keystone,klmitch/keystone,JioCloud/keystone,cloudbau/keystone,himanshu-setia/keystone,promptworks/keystone,rajalokan/keystone,dims/keystone,rodrigods/keystone,blueboxgroup/keystone,reeshupatel/demo,cloudbau/keystone,nuxeh/keystone,citrix-openstack-build/keystone,cernops/keystone,ntt-sic/keystone,ging/keystone,ajayaa/keystone,ajayaa/keystone,promptworks/keystone,nuxeh/keystone,ilay09/keystone,cloudbau/keystone,townbull/keystone-dtrust,ging/keystone,jumpstarter-io/keystone,rickerc/keystone_audit,takeshineshiro/keystone,maestro-hybrid-cloud/keystone,derekchiang/keystone,jamielennox/keystone,ntt-sic/keystone,rickerc/keystone_audit,derekchiang/keystone,maestro-hybrid-cloud/keystone,ilay09/keystone,UTSA-ICS/keystone-kerberos,openstack/keystone,cernops/keystone,mahak/keystone,townbull/keystone-dtrust,dsiddharth/access-keys,jonnary/keystone,citrix-openstack-build/keystone,rajalokan/keystone,reeshupatel/demo,promptworks/keystone,openstack/keystone,rushiagr/keystone,vivekdhayaal/keystone,openstack/keystone,jonnary/keystone,nuxeh/keystone,dstanek/keystone,ntt-sic/keystone,roopali8/keystone,MaheshIBM/keystone,JioCloud/keystone,jumpstarter-io/keystone,mahak/keystone,dsiddharth/access-keys