MFC r310257: Improve support for informational exceptions.

MFC r310257: 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.

git-svn-id: svn://svn.freebsd.org/base/stable/10@311403 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f