Description of problem:

During deployment of a VNF via heat stack, it failed with ERROR:

2019-12-30 18:01:10Z [IMS_Ericsson_BGF.PL_scaling_group]: CREATE_FAILED ResourceInError: resources.PL_scaling_group.resources[0].resources.scaled_vm.resources[0]: Went to status ERROR due to "Message: Host 'overcloud-compute' is not mapped to any cell, Code: 400"
2019-12-30 18:01:10Z [IMS_Ericsson_BGF]: CREATE_FAILED Resource CREATE failed: ResourceInError: resources.PL_scaling_group.resources[0].resources.scaled_vm.resources[0]: Went to status ERROR due to "Message: Host 'overcloud-compute' is not mapped to any cell, Code: 400"

Environment:
Red Hat OpenStack Platform release 13.0.7 (Queens)
openstack-tripleo-heat-templates-8.3.1-54.el7ost.noarch
openstack-nova-api-17.0.10-1.el7ost.noarch                  Thu Dec  5 18:47:46 2019
openstack-nova-common-17.0.10-1.el7ost.noarch               Thu Dec  5 18:47:37 2019
openstack-nova-compute-17.0.10-1.el7ost.noarch              Thu Dec  5 18:47:37 2019
openstack-nova-conductor-17.0.10-1.el7ost.noarch            Thu Dec  5 18:47:46 2019
openstack-nova-scheduler-17.0.10-1.el7ost.noarch            Thu Dec  5 18:47:46 2019

How reproducible:
The steps made by customer which leaded into the issue are:

1) OSP upgrade from 12 to 13.

2) New compute added to Overcloud after upgrade to 13 is completed.

3) Deploy VNF using new compute.

Actual results:
VNF deployment fails with ERROR "Message: Host 'overcloud-compute' is not mapped to any cell, Code: 400"

Expected results:
VNF deployed successfully.

Additional info:
Customer solved the issue by executing following command in controller:
# docker exec nova_api /bin/bash -c '/usr/bin/nova-manage cell_v2 discover_hosts --verbose'

Same ERROR than reported in BZ 1480326.