Better command line help for benchmarks

The new benchmarks are using the Google Benchmark library and inheriting its command line arguments. If you don't know the Google Benchmark library very well, it is difficult to know how to control the benchmarks (such as changing formats and selecting which benchmarks to run). Unfortunately, simply using the --help argument does not provide much useful information.

kmorel2 1> ./BenchmarkArrayTransfer --help
Usage information:

  --device, -d <dev>                  Force device to dev. Omit device to list
                                      available devices.
  -v <#|INFO|WARNING|ERROR|FATAL|OFF> Specify a log level (when logging is
                                      enabled).
  --help, -h                          Print usage information.