Create a new image by taking a snapshot of a running server and download the image.
nova image-create instance_name image_name glance image-download image_name --file exported_vm.qcow2
Upload the exported image into glance in Overcloud and launch a new instance.
glance image-create --name imported_image --file exported_vm.qcow2 --disk-format qcow2 --container-format bare nova boot --poll --key-name default --flavor m1.demo --image imported_image --nic net-id=net_id imported
Warning: disadvantage of using glance image for export/import VMs is that each VM disk has to be copied in and out into glance in source and target clouds. Also by making snapshot qcow layering system is lost.