Compare two bootcharts and list timestamps for selected processes.

Usage: system/core/init/compare-bootcharts.py base_bootchart_dir
       exp_bootchart_dir

For example, here is the output where the bootanimation is changed
from "d 0 0 part2" to "c 0 0 part2":

--

process: baseline experiment (delta)
 - Unit is ms (a jiffy is 10 ms on the system)
------------------------------------
/init: 50 40 (-10)
/system/bin/surfaceflinger: 4320 4470 (+150)
/system/bin/bootanimation: 6980 6990 (+10)
zygote64: 10410 10640 (+230)
zygote: 10410 10640 (+230)
system_server: 15350 15150 (-200)
bootanimation ends at: 33790 31230 (-2560)

--

In this example bootanimation is finished (estimated) 2.56 seconds sooner.

Change-Id: I39d59897c8c53d7d662676813e884b9d58feec3c