tests: add worker count to class description
tests: add worker count to class description

While running test:

==============================================================================
NAT44ED Test Case
==============================================================================

==>

==============================================================================
NAT44ED Test Case [main thread only]
==============================================================================

==============================================================================
NAT44ED Test Case [1 worker thread]
==============================================================================

==============================================================================
NAT44ED Test Case [4 worker threads]
==============================================================================

Type: improvement
Signed-off-by: Klement Sekera <b8003f27414ca85c37624503b7b4e8f8c829bb4d@cisco.com>
Change-Id: I61904b411ff1b58700564698079dc4c07cea5c5e

FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp