Support ARM architecture

[xunholy]

Currently, the weave CNI supports ARM architecture, however, when trying to set up the cloud agent I noticed it does not support multiple architectures.

Also when attempting to do cross-compile locally it was quite painful due to having to build the binary locally then copy things around and after all, this is done then to copy the binary into the image, I would like to suggest placing this build logic into a multistage Dockerfile - I'd be happy to invest some time to do this if you'd be open to this adaption?

[jonwilliams84]

Is there any update to this, ARM64 support would be the icing on the cake to what already looks like a superb tool.