ps3enc.py: move cleanup leg
include audio tracks in __str__ method
video_source.py: use proper option parser code.
ps3enc.py: clean-up verbosity
ps3enc.py: refit argument parsing code with argparse

This makes the usage text auto-generated from the options. I also
cleaned up the mencoder calling functions a little to wrap them up in
an object. This was mainly to avoid getting ugly with passing args around.
ps3enc.py: allow valgrinding of child.
ps3enc.py: move print across to logging statements
libs: push logger into the work classes.
libs: use common run_cmd function