Docker machine qemu driver

I needed a non-libvirt qemu driver, so this is it.

from @SvenDowideit

Its initial use is going to be for running the Rancher OS tests, but maybe you'll find a use for it too.

from @fventuri

QEMU

Create machines locally using QEMU. This driver requires QEMU to be installed on your host.

$ docker-machine create --driver=qemu qemu-test

Options:

• --qemu-boot2docker-url: The URL of the boot2docker image. Defaults to the latest available version.
• --qemu-disk-size: Size of disk for the host in MB. Default: 20000
• --qemu-memory: Size of memory for the host in MB. Default: 1024
• --qemu-cpu-count: Number of CPUs. Default: 1
• --qemu-program : Name of the qemu program to run. Default: qemu-system-x86_64
• --qemu-display : Show the graphical display output to the user. Default: false
• --qemu-display-type : Select type of display to use (sdl/vnc=localhost:0/etc)
• --qemu-nographic : Use -nographic instead of -display none. Default: false
• --qemu-virtio-drives : Use virtio for drives (cdrom and disk). Default: false
• --qemu-network: Networking to be used: user, tap or bridge. Default: user
• --qemu-network-interface: Name of the network interface to be used for networking. Default: tap0
• --qemu-network-address: IP of the network address to be used for networking.
• --qemu-network-bridge: Name of the network bridge to be used for networking. Default: br0

The --qemu-boot2docker-url flag takes a few different forms. By default, if no value is specified for this flag, Machine will check locally for a boot2docker ISO. If one is found, that will be used as the ISO for the created machine. If one is not found, the latest ISO release available on boot2docker/boot2docker will be downloaded and stored locally for future use. Note that this means you must run docker-machine upgrade deliberately on a machine if you wish to update the "cached" boot2docker ISO.

This is the default behavior (when --qemu-boot2docker-url=""), but the option also supports specifying ISOs by the http:// and file:// protocols. file:// will look at the path specified locally to locate the ISO: for instance, you could specify --qemu-boot2docker-url file://$HOME/Downloads/rc.iso to test out a release candidate ISO that you have downloaded already. You could also just get an ISO straight from the Internet using the http:// form.

Note that when using virtio the drives will be mounted as /dev/vda and /dev/vdb, instead of the usual /dev/cdrom and /dev/sda, since they are using paravirtualization.

If using the real network (tap or bridge), note that it needs a DHCP server running. The user network has it's own NAT network, which usually means it is running on 10.0.2.15 Ultimately this driver should be able to query for IP, but for now the workaround is to use --qemu-network-address (and fixed addresses) until that feature is implemented.

Environment variables:

Here comes the list of the supported variables with the corresponding options. If both environment variable and CLI option are provided the CLI option takes the precedence.

Environment variable	CLI option
QEMU_BOOT2DOCKER_URL	--qemu-boot2docker-url
QEMU_VIRTIO_DRIVES	--qemu-virtio-drives