plot_utils: Fix nr_runs typo

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
plot_utils: Stack dump on error

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
plot_utils: Rearrange text outside of the plot

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
plot_utils: Fix parallel rendering

Try 10 times before throwing an actual exception. matplotlib seems to
have some issues with parallel plotting. If it doesn't work the first
time it very likely will work the next time savefig is called.

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
plot_utils: Close figure after saving it

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>