Add method get_bin_path to module_common.py

[sfromm]

This is meant to assist all the modules that look for the full path of
an executable. If it is found and is X_OK, returns the full path.
Otherwise, it returns None.

[mpdehaan]

Looks good.

I'll take this if you can update this to make some modules use it, that way it just doesn't sit there unused.

Thanks!