build: use /usr/bin/env to call python

Hardcoding the path to python instead of env is not recommended.  This
can break the build in some Linux environments that link /usr/bin/python
to python3.

Change-Id: I4c62eb391acc6d468ce24ac8640834e965e76e78
Merge remote-tracking branch 'cm/cm-11.0' into cm-11.0