pybootchartgui: split the output chart into multiple ones
Split the output chart into multiple ones to make it more readable, it
only works with "-o path", which means that it doesn't work if the user
doesn't want to save the chart to the disk. For example:
$ ./pybootchartgui.py /path/to/tmp/buildstats/core-image-sato-qemux86/
201205301810/ -f svg -s 5 -o /tmp/
bootchart written to /tmp/bootchart_1.svg
bootchart written to /tmp/bootchart_2.svg
bootchart written to /tmp/bootchart_3.svg
bootchart written to /tmp/bootchart_4.svg
bootchart written to /tmp/bootchart_5.svg
[YOCTO #2403]
Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
