Run scan-view on systems with python3 as default python provider

[raj.khem]

Summary

Linux Distros e.g. archlinux have started to use python3 as default python interpreter, therefore we need to be specific if we need python2

[raj.khem]

it works with python3 too, perhaps it would be good to ask for python3 instead

tools/scan-view/bin/scan-view

-#!/usr/bin/env python
+#!/usr/bin/env python2
 
 """The clang static analyzer results viewer.
 """