Comment 4 for bug 1708039

I'm not sure why discover_hosts isn't being run from devstack-gate, but grenade will run 'nova-manage cell_v2 simple_cell_setup' which will create the cell0 and cell1 mappings, sync the db for cell0, and discover compute hosts:

http://logs.openstack.org/54/489754/3/check/gate-grenade-dsvm-neutron-multinode-ubuntu-xenial/7e19ce3/logs/grenade.sh.txt.gz#_2017-08-01_21_52_05_564

2017-08-01 21:52:05.564 | + lib/nova:create_cell:956 : nova-manage cell_v2 simple_cell_setup --transport-url rabbit://stackrabbit:secretrabbit@10.16.232.107:5672/

That runs 4 minutes before the subnode compute node record is created, so that's why it's not mapped to cell1 and anything trying to use it fails.