twister: harness: Fix TestCase id at Console for Ztest

Implement a workaround for Console harness to compose TestCase
identifier correctly when a Ztest suite with a single testcase
uses this harness type. Normally, a Ztest suite should use the
Ztest Twister harness.
Without this workaround each Ztest TestCase result on Console is
duplicated (and written into twister.json) with its 'identifier'
attribute set to TestSuite id only, no TestCase suffix added;
the resulting entry with the full TestCase id is also stored,
but its values are empty with defaults.

Signed-off-by: Dmitrii Golovanov <dmitrii.golovanov@intel.com>