Use /usr/bin/env python instead of /usr/bin/python

The usage of /usr/bin/env ensures that the first interpreter
found in the environment's $PATH variable is used. This should
be preferred.

Change-Id: Ifca0c47f2d1b123b4d5f9fb5e98191262ed25bca
Merge "Use /usr/bin/env python instead of /usr/bin/python"