Support overriding OPENTRACING_INCLUDE_DIR and OPENTRACING_LIBRARY
Support overriding OPENTRACING_INCLUDE_DIR and OPENTRACING_LIBRARY

lightstep/lightstep-tracer-cpp,lightstep/lightstep-tracer-cpp,lightstep/lightstep-tracer-cpp,lightstep/lightstep-tracer-cpp,lightstep/lightstep-tracer-cpp