Comment 2 for bug 1169150

This patch removes -xpickle value from option -u and provides the additional fixes:
- redirects stderr to /dev/null when stopping apport to not exit the test if apport is already stopped
- Run the the under debian/script.py to fix stdin indirection imposed by adt-run
- debian/scripts.py waits for the child process to exit and exit with its return code.