battery_bench: make log time start at 0 (since plugin started)

Print current rockbox uptime when the plugin was started
Make some lines start with '#' so they are not plotted by gnuplot

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@27339 a1c6a512-1295-4272-9138-f99709370657
1 file changed