[meta-virtualization] docker-proxy links against host libraries

[Pascal Bach]

Hello

I observed some strange linking problem with the "docker-proxy" when building for qemux86-64.

It seems that the binary is linked against the host version of

```
$ file image/usr/bin/docker-proxy
image/usr/bin/docker-proxy: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, not stripped
                                                                                                                 ^^^^^^
```

I only noticed the issue on my build as it is a multi lib Debian where the libraries are under /lib64 and /lib32.
However on the target there there is only /lib to the binary did not work there.

Only the docker-proxy binary is affected by this, the other binaries (docker, dockerd) are fine.

```
$ file image/usr/bin/docker
image/usr/bin/docker: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=c118d2393c7932172ca3e183bb304fe1cff73ce5, not stripped
```

I tried to fix the recipe by replacing the build command for docker-proxy [1] with the following line:

```
${GO} build ${GOBUILDFLAGS} -o ${S}/src/import/docker-proxy github.com/docker/libnetwork/cmd/proxy
```

But without success the linked loader is still wrong.

It is also worth mentioning that this only happens with x86_64 builds (tried: qemux86-64, genericx64-64) but not with other architectures like armv7.
I was also able to reproduce this on poky master today (commit: 9ed34e315a8d2db58e212b0770dfa8f4ad00f637).


The only solution I found so far is to put the docker-proxy into a separate recipe and add it as a RDEPENDS to docker.
I will submit a patch for this and you can decide if this would be an acceptable solution.

Regards
Pascal

[1] https://git.yoctoproject.org/cgit/cgit.cgi/meta-virtualization/tree/recipes-containers/docker/docker_git.bb#n119