Use an appropriate ``extract_traceback`` limit

When looking for where this modules ``run/load`` ends and
the user code begins we only need to search back at most
three levels to find this information; so to avoid getting
many more frames (especially when they won't be used) then
we need to just apply a sensible limit on the levels we get.

Change-Id: I9186e8844c92697b7e3f850328b6b39afba0150d
Merge "Use an appropriate ``extract_traceback`` limit"