ftrace: fix error when compare runs

When compare multiple run instances, need convert axis objects from 2D array type to 1D array type; in the code it use zip() to do the conversion. But when every run instance has only one actor, then it will directly return back axis object with 1D array type, so zip function will report failure.

This patch is to check if axis is 2D array, and will convert it to 1D array.

Signed-off-by: Leo Yan leo.yan@linaro.org