magnum: Use type=simple for openstack-magnum-api.service
magnum: Use type=simple for openstack-magnum-api.service

magnum-api does not support SD_NOTIFY so starting the service hangs
when using type=notify.
Note: mangum-conductor *does* support SD_NOTIFY so keep the type there.

Change-Id: Idd40b0df8c2215bb5ae95c5fb5ef4c2496cdbd12

openstack/rpm-packaging,openstack/rpm-packaging