[OSP14] After successful scale out, live/cold migration and resize fails to the new added compute with 'Host key verification failed'

Issue

After successful scale out procedure, live_migration (unless TLS) or cold-migration fail with an ssh host key verification error when instances get migrated to the new compute nodes. A live migration error Live Migration failure: operation failed: Failed to connect to remote libvirt URI qemu+ssh://nova_migration@compute-1.internalapi.localdomain:2022/system?keyfile=/etc/nova/migration/identity: Cannot recv data: Host key verification failed.: Connection reset by peer is reported in the nova-compute log.

In the nova compute log the following error is shown /var/log/containers/nova/nova-compute.log

2019-01-07 22:01:10.568 1 ERROR nova.virt.libvirt.driver [-] [instance: d3e55f05-461c-452f-ada0-7ff30ea6cdf2] Live Migration failure: operation failed: Failed to connect to remote libvirt URI qemu+ssh://nova_migration@compute-1.internalapi.localdomain:2022/system?keyfile=/etc/nova/migration/identity: Cannot recv data: Host key verification failed.: Connection reset by peer: libvirtError: operation failed: Failed to connect to remote libvirt URI qemu+ssh://nova_migration@compute-1.internalapi.localdomain:2022/system?keyfile=/etc/nova/migration/identity: Cannot recv data: Host key verification failed.: Connection reset by peer
2019-01-07 22:01:10.569 1 DEBUG nova.virt.libvirt.driver [-] [instance: d3e55f05-461c-452f-ada0-7ff30ea6cdf2] Migration operation thread notification thread_finished /usr/lib/python2.7/site-packages/nova/virt/libvirt/driver.py:7489
2019-01-07 22:01:10.632 1 DEBUG nova.virt.libvirt.migration [-] [instance: d3e55f05-461c-452f-ada0-7ff30ea6cdf2] VM running on src, migration failed find_job_type /usr/lib/python2.7/site-packages/nova/virt/libvirt/migration.py:355
2019-01-07 22:01:10.632 1 DEBUG nova.virt.libvirt.driver [-] [instance: d3e55f05-461c-452f-ada0-7ff30ea6cdf2] Fixed incorrect job type to be 4 _live_migration_monitor /usr/lib/python2.7/site-packages/nova/virt/libvirt/driver.py:7305
2019-01-07 22:01:10.633 1 ERROR nova.virt.libvirt.driver [-] [instance: d3e55f05-461c-452f-ada0-7ff30ea6cdf2] Migration operation has aborted

Note: this also affects instance resize actions as it involves a migration.