Ensure manager grant methods throw exception if role_id is invalid.
Ensure manager grant methods throw exception if role_id is invalid.

We currently don't test whether the assignment manager/driver
grant methods correctly throw a RoleNotFound exception if the role
is invalid. This patch adds a test for this.

Such a test will be useful to ensure this functionality is
maintained as we migrate roles to their own backend.

Change-Id: I51e87129fb3efcc1abae9c59915eaca38eb91227
Closes-bug: 1406721

takeshineshiro/keystone,rajalokan/keystone,ajayaa/keystone,klmitch/keystone,maestro-hybrid-cloud/keystone,MaheshIBM/keystone,roopali8/keystone,rushiagr/keystone,dstanek/keystone,rajalokan/keystone,cernops/keystone,openstack/keystone,maestro-hybrid-cloud/keystone,idjaw/keystone,ajayaa/keystone,mahak/keystone,blueboxgroup/keystone,rushiagr/keystone,ilay09/keystone,nuxeh/keystone,blueboxgroup/keystone,MaheshIBM/keystone,roopali8/keystone,jumpstarter-io/keystone,dstanek/keystone,cernops/keystone,vivekdhayaal/keystone,promptworks/keystone,promptworks/keystone,dims/keystone,jamielennox/keystone,jumpstarter-io/keystone,jonnary/keystone,vivekdhayaal/keystone,jonnary/keystone,jamielennox/keystone,nuxeh/keystone,openstack/keystone,himanshu-setia/keystone,idjaw/keystone,takeshineshiro/keystone,himanshu-setia/keystone,dims/keystone,vivekdhayaal/keystone,nuxeh/keystone,promptworks/keystone,jumpstarter-io/keystone,mahak/keystone,ilay09/keystone,rajalokan/keystone,UTSA-ICS/keystone-kerberos,openstack/keystone,mahak/keystone,UTSA-ICS/keystone-kerberos,dstanek/keystone,klmitch/keystone,ilay09/keystone,rushiagr/keystone