Reduce severity of generic discrete assert to 'Ok'

In practice, generic discrete sensors have not indicated good *or* bad
health They have most commonly been used to indicate something like a
particular option being available or user disabled.  This does mean
that something trying to use an utterly generic discrete sensor will
not trigger a health issue, but hopefully those cases leverage more
informative events that do have clear 'health' connotations.  There
remains the chance that a sensor will rely upon the vocabulary of
the text in SDR and that just cannot be avoided.

Change-Id: I777b2f1300301291ca5a3aa7a6b18de1de6f9d1a