log: bug fix register class compare mismatch
log: bug fix register class compare mismatch

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 <ab7ded68d87ed0802502347b3f94ef8c2393e921@ericsson.com>

FDio/vpp,vpp-dev/vpp,vpp-dev/vpp,FDio/vpp,vpp-dev/vpp,FDio/vpp,vpp-dev/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,vpp-dev/vpp,chrisy/vpp,chrisy/vpp,vpp-dev/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,vpp-dev/vpp