tools: exclude benchmark code from coverage report
Refs: https://github.com/nodejs/build/issues/1676#issuecomment-459218651
Checklist
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make -j4 test(UNIX), orvcbuild test(Windows) passes -
commit message follows commit guidelines
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Refs: https://github.com/nodejs/build/issues/1676#issuecomment-459218651
make -j4 test (UNIX), or vcbuild test (Windows) passes