Create a virtual machine instance with the qemu-kvm command, and create a virtual bridge and network interface with the brctl command
The bottom layer of the openstack horizon interface also calls these commands (ovs) to create instances and network devices (bridges and network interfaces)
Reference: http://www.cnblogs.com/CloudMan6/p/6287658.html
https://blog.csdn.net/jackliu16/article/details/79542405
https://blog.csdn.net/jackliu16/article/details/80072992
