cardiff: Upgrading bottom line to 2% for CPU diff

When comparing CPU's speed & performance, we shall ignore differences
smaller than 2% of the global result, unless we get some very weird
curious perf.

2% is good enough.

Before:
Group 1 : Checking CPU perf
bogomips                          : SUMMARY :  15 consistent hosts with  4000.23    as average value and     0.53 standard deviation
loops_per_sec                     : SUMMARY :  13 consistent hosts with   453.42    as average value and     0.35 standard deviation
loops_per_sec                     : SUMMARY :   2 curious    hosts with   454.69    as average value and     0.03 standard deviation
CPU Efficiency                    : SUMMARY :  15 consistent hosts with    75.72 %  as average value and     0.29 standard deviation

After:
Group 1 : Checking CPU perf
bogomips                          : SUMMARY :  15 consistent hosts with  4000.23    as average value and     0.53 standard deviation
loops_per_sec                     : SUMMARY :  15 consistent hosts with   453.59    as average value and     0.54 standard deviation
CPU Efficiency                    : SUMMARY :  15 consistent hosts with    75.72 %  as average value and     0.29 standard deviation