Added DriverFailure exception
Added DriverFailure exception

A driver failure exception can be raised from any driver module. When
raising such an exception, the driver needs to fill in 'driver' as the
driver name and 'exc' as a textual representation of the original
exception.

tengqm/senlin-container,stackforge/senlin,Alzon/senlin,openstack/senlin,tengqm/senlin,stackforge/senlin,tengqm/senlin,openstack/senlin,Alzon/senlin,tengqm/senlin-container,openstack/senlin