Log kwargs on a failed String Format Operation
Log kwargs on a failed String Format Operation

fixes bug 971552

If the string format operation in NovaException raises an exception be sure to
log the kwargs at log level error

Change-Id: Idfc54b8c05256bd7c849c86dc45f0b493727fe58

openstack/oslo.versionedobjects,citrix-openstack-build/oslo.versionedobjects