The current code had broken exception handling due to the use of a
"traceback" variable as well as an import. Use the new library code
for this instead which reduces code duplication and has fixed/improved
exception handling.
The chdir code can be dropped since any directory changes are in other
processes now so there is no need for it here and the code no longer
changes directory.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
