scripts: Don't hardcode /usr/bin/python
scripts: Don't hardcode /usr/bin/python

But use /usr/bin/env python in the shebang. This obviously allows the
script to work in environments where python is not installed in /usr/bin
say, on Windows where it's somewhere in the system outside of the msys fs.

GNOME/clutter-gst,lubosz/clutter-gst,ystreet/clutter-gst,lubosz/clutter-gst,GNOME/clutter-gst,ystreet/clutter-gst,skinkie/clutter-gst,GNOME/clutter-gst,ystreet/clutter-gst,skinkie/clutter-gst,lubosz/clutter-gst,skinkie/clutter-gst,GNOME/clutter-gst,ystreet/clutter-gst