Improve support for informational exceptions.

While CTL still has no real events to report in this way (like SMART),
it is possible to trigger false event by manually setting TEST bit in
Informational Exceptions Control mode page, that can be useful for
initiator testing. This code supports all flavours of IE reporting:
UNIT ATTENTION, RECOVERED ERROR and NO SENSE sense keys, REQUEST SENSE
command and Informational Exceptions log page.

MFC after: 2 weeks
Sponsored by: iXsystems, Inc.