If you are using packstack the deploy it. the virt type shall be depend on host. Below is answer file configuration.

# The hypervisor driver to use with Nova. Can be either 'qemu' or
# 'kvm'. Defaults to 'qemu' on virtual machines and 'kvm' on bare
# metal hardware. For nested KVM set it explicitly to 'kvm'.
CONFIG_NOVA_LIBVIRT_VIRT_TYPE=%{::default_hypervisor}

But it may choose the Qemu but not KVM, so you can directly change the /etc/nova/nova.conf

[libvirt]
# Libvirt domain type (string value)
# Allowed values: kvm, lxc, qemu, uml, xen, parallels
#virt_type=kvm

Or you can modify the code as below:

https://review.openstack.org/#/c/393254/5/nova/virt/libvirt/driver.py