cardiff: Adding bogomips support to perf_cpu_tables

For checking cpu perf, we can use both loops_per_sec and bogomips. So
let's make a generic function that works for both.
cardiff: Checking CPU perf if group is stable

If the group is stable, let's check if the performance is as good as
expected, if not let's print a warning or an error.

A typical output looks like :

Group 0 : Checking CPU perf
bogomips                          : SUMMARY :   1 consistent hosts with  3999.92    as average value and     0.00 standard deviation : PERF FAIL as min perf should have been : 4000
loops_per_sec                     : SUMMARY :   1 consistent hosts with   453.28    as average value and     0.00 standard deviation : PERF FAIL as min perf should have been : 456
CPU Efficiency                    : SUMMARY :   1 consistent hosts with    75.83 %  as average value and     0.00 standard deviation

Group 1 : Checking CPU perf
bogomips                          : SUMMARY :  15 consistent hosts with  4000.23    as average value and     0.53 standard deviation : PERF OK
loops_per_sec                     : SUMMARY :  15 consistent hosts with   453.59    as average value and     0.54 standard deviation : PERF FAIL as min perf should have been : 456
CPU Efficiency                    : SUMMARY :  15 consistent hosts with    75.72 %  as average value and     0.29 standard deviation

Group 2 : Checking CPU perf
bogomips                          : SUMMARY :   3 consistent hosts with  3999.95    as average value and     0.01 standard deviation : PERF FAIL as min perf should have been : 4000
loops_per_sec                     : SUMMARY :   3 consistent hosts with   453.80    as average value and     0.41 standard deviation : PERF FAIL as min perf should have been : 456
CPU Efficiency                    : SUMMARY :   3 consistent hosts with    75.73 %  as average value and     0.35 standard deviation

Note that PERF OK and PERF FAIL are printed in GREEN & RED colors respectively.