Set up a port with a fixed address, then launch your instance on this port:

neutron port-create .... --fixed-ip subnet_id=SUBNET,ip_address=IP_ADDR .....
nova boot .... nic port_id=....

or simply provide the IP address in the nova boot command

nova boot .... --nic <net-id=net-uuid,v4-fixed-ip=ip-addr ....

See also: neutron CLI reference and nova CLI reference

Create a neutron port with fixed IP on a specific network,subnet -

neutron port-create --fixed-ip subnet_id=<subnet_id>,ip_address=<fixed_ip> --name flat-port-subnet1 <net_id>

launch the VM with nova command and using '--port-id' to get the above mentioned fixed IP address