Minimize official execution time of benchmark for established production systems

[maherou]

HPCG can be run to completion in a few minutes, if we keep the number of sets low. We should have a rapid execution mode that permits a valid result to be produced in a short amount of time.

Originally HPCG was intended to be run for a long time. This is not feasible for installed production systems where they have little time when the whole machine is available. We should permit short execution times for established production systems.

[maherou]

If the runtime (specified either in BUILD_DIR/bin/hpcg.data or using the --rt command line argument) is set to 0 (zero), all multiple execution loop sets will be set to one, minimizing the execution time for all phases of HPCG. This feature can also be used for debugging and profiling.