SSD perf multi-tier benchmarking experiments

[byrnedj]

In this issue we report SSD perf experiments with the graph_cache_leader workload

SSD perf experiments
Workload: ssd_perf/graph_cache_leader

1. 4.1B keys - default power is 26, test with 30 htBucketPower and 30 htLockPower
   The combinations are (26,26) and (30,30), the total number of experiments are 6 (1 workload * 2 configs * 3 versions).
2. Ratio of DRAM:PMEM - 1:1, 1:4, 1:8
   The total number of experiments are 3 (1 workload * 3 configs * 1 version - multi tier only).

CacheLib versions to test

1. Multi-tier reduced critical section - once ratio bug has been fixed.
2. DRAM single tier
3. PMEM single tier