binfmt-register docker image for arm/aarch64

The purpose of the image is to run arm/aarch64 docker image in x86-64 plaform. It also can be used in building arm/aarch64 image. I made an example yen3/docker-ubuntu-novnc. You can see the project to get more details.

If you use Docker in macOS, you have no need to use the docker image since the macOSX docker has hypervisor inside.

Requirement

docker with privileged access for binfmt_misc register.

Get the image

Command memo
```
docker pull yen3/binfmt-register:latest
```

Usage

Command example (in Ubuntu 16.04). You can replace the first two lines with export CPU=aarch64 and export RUN_IMAGE=arm64v8/alpine to test aarch64

export CPU=arm
export RUN_IMAGE=arm32v7/alpine

# Register binfmt
docker run --rm --privileged yen3/binfmt-register set ${cpu}

# Get qemu static binary
docker run --rm yen3/binfmt-register get ${cpu} > qemu-${cpu}-static
chmod +x qemu-${cpu}-static

# Run the image with the qemu static binary
export MOUNT_QEMU="-v $(pwd)/qemu-${cpu}-static:/usr/local/bin/qemu-${cpu}-static"
docker run -it --rm ${MOUNT_QEMU} ${RUN_IMAGE} uname -a

# Unregister binfmt
docker run --rm --privileged yen3/binfmt-register clear ${cpu}

# Remove the qemu static binary
rm -f qemu-${cpu}-static

Other example

test.sh provides a simple example for running arm/aarch64 docker images in Linux and Darwin(macOS) platform
The makefile and dockerfiles in yen3/docker-ubuntu-novnc provide an example to build arm/aarch64 docker images in Linux/Darwin platform.

Build the docker image

Build command: docker build -t yen3/binfmt-register:latest
- The source of qemu static binary is from qemu-* package in alpine:edge. The version of qemu is 2.10.
If you have any need to build qemu static binary from source. The example dockerfile is in from_source/Dockerfile. The build command is
```
docker build -t yen3/binfmt-register:latest -f from_source/Dockerfile
```