These periodic jobs are failing, let's disable the periodic jobs.
They have been broken since ages without fixing. There's no
record of a successful run under Zuul v3.
Last images at http://tarballs.openstack.org/magnum/images/ are from
2017.
This only backports the disabling of the jobs.
Change-Id: I01122fa029b4124d912e80ea43bca07b8f2ebe5c
(cherry picked from commit 42c75c4d3d)