Resources required to delete a pool affect subsequent test run

Many benchmarks delete and recreate the test pool between runs. However, the Ceph command to delete a pool returns immediately, and the work of deleting objects in the pool takes place in the background. Unfortunately, experience has shown that disk and CPU resources used while deleting the objects is great enough that it influences the test results for the subsequent run.

One way to avoid the problem is to have the cluster.rmpool() function wait until the disk and CPU utilization on the OSD nodes drops to a reasonable level before returning to the caller. I will be issuing a pull request with this change.