Revamp benchmark tests

1. Move to a time-based (60s) benchmark to avoid these taking an absurd
amount of time to show the same information.

2. Eliminate the 256k random benchmarks, since they don't really add
anything.

3. Add in a 4k single-queue benchmark as this might provide valuable
insight into latency.

4. Adjust the output to reflect the above changes.

While this does change the benchmarking, this should not invalidate any
existing benchmarks since most of the test suit is unchanged (especially
the most important 4M sequential and 4K random tests). It simply removes
an unused entry and adds a more helpful one. The time-based change
should not significantly affect the results either, just reduces the
total runtime for long-tests and increase the runtime for quick tests to
provide a better picture.

client-cli/pvc/pvc.py

@@ -2526,7 +2526,7 @@ def ceph_benchmark_run(pool):
     Run a storage benchmark on POOL in the background.
     """
     try:
-        click.confirm('NOTE: Storage benchmarks generate significant load on the cluster and can take a very long time to complete on slow storage. They should be run sparingly. Continue', prompt_suffix='? ', abort=True)
+        click.confirm('NOTE: Storage benchmarks take approximately 8 minutes to run and generate significant load on the storage cluster; they should be run sparingly. Continue', prompt_suffix='? ', abort=True)
     except Exception:
         exit(0)