cardiff: Adding minimum variance check

We shall not try to find the black sheep if the variance is below a
certain value. This patch add a tolerance_min inside the print_perf() to
avoid useless warnings.
cardiff: Adding memory benchmark analysis

This commit check all the memory benchmarks and compute them.

The analysis is done for the 1K, 4k, 1M, 16M, 128M, 1G and 2G values.

A typical output looks like for the 1M block size is :

Memory benchmark 1M             : INFO    : logical_8    : Group performance : min= 8886.00, mean= 8894.00, max= 8903.00, stddev=    4.21
Memory benchmark 1M             : INFO    : logical_8    : Group performance = 8894.00   : CONSISTENT
Memory benchmark 1M             : INFO    : logical_9    : Group performance : min= 8886.00, mean= 8897.67, max= 8910.00, stddev=    5.97
Memory benchmark 1M             : INFO    : logical_9    : Group performance = 8897.67   : CONSISTENT
Memory benchmark 1M             : INFO    : Thread effi. : Group performance : min=   21.87, mean=   22.53, max=   23.26, stddev=    0.38
Memory benchmark 1M             : INFO    : Thread effi. : Group performance =   22.53   : CONSISTENT
Memory benchmark 1M             : INFO    : Forked Effi. : Group performance : min=   40.82, mean=   40.99, max=   41.11, stddev=    0.09
Memory benchmark 1M             : INFO    : Forked Effi. : Group performance =   40.99 % : CONSISTENT
cardiff: Improve printing

This makes the field a little bit bigger and also consider all
efficiency computation as percentage.