Handle comma separated decimals in mpstat output

Workaround replacing commas resulting from a German like locale with dots. Previously given message: "mpstat Exception: invalid literal for float(): 0,00"

Actually using some locale setting might be better, but I have no time to check side effects, and this workaround should be free of such.
Merge pull request #223 from felix-kolbe/patch-1

Handle comma-formatted decimals in mpstat output (like in a German locale).