core: audit log unknown values

Previous fix renamed the "unknown" to "non-interactive user"... however,
that doesn't fit the needs, as this value is being used for generic
issues, so "unknown" is a better fit.

Change-Id: Id77e70f09a05e57ee00718de1c925a9e90c48b4b
Bug-Url: https://bugzilla.redhat.com/1123828
Signed-off-by: Oved Ourfali <oourfali@redhat.com>