1. Otherwise, the log classes with same prefix, e.g. "abc" and
"abc-de" will all be registered into log class "abc";
2. Minor improvement for test log help string.
Change-Id: I8d93be5e8fa67db6012198b3442a9e2bddcb744a Signed-off-by: Su Wang <su.z.wang@ericsson.com>