CBQE=0: export C_FORCE_ROOT for new celery version 3.1.16

Change-Id: I72f47015de7d99f8bd739df92db1dfc885dae2d4
Reviewed-on: http://review.couchbase.org/43075
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>
Tested-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>