cardiff: Adding rampup mode

This mode aims at analyzing the output of AHC ran into a distributed
mode with a rampup.

Like if you want to understand how a set of VMs from 1 to 81 performed,
you can use the --rampup mode on the resulting directory.

cardiff.py -r '/var/lib/edeploy/health/dahc/mycombinedtest/2014_09_15-12h17'

It has been tested on cpu & memory test.