This is to resolve the following issue in CI:

    c/_cffi_backend.c:15:17: fatal error: ffi.h: No such file or directory
     #include <ffi.h>
                     ^
    compilation terminated.
    error: command 'gcc' failed with exit status 1
    ----------------------------------------
ERROR: Command errored out with exit status 1: /home/zuul/kayobe-venv/bin/python -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-PV3WhJ/cffi/setup.py'"'"'; __file__='"'"'/tmp/pip-install-PV3WhJ/cffi/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' install --record /tmp/pip-record-ZvlZVY/install-record.txt --single-version-externally-managed --compile --install-headers /home/zuul/kayobe-venv/include/site/python2.7/cffi Check the logs for full command output.

Change-Id: I1bd724be7dc77058870f37cb1c9404472fa466ca
see: https://zuul.opendev.org/t/openstack/build/c20a316a699b4073abf75960634ebfcd