Build inside the build container, using go1.5, by default

[tomwilkie]

Fixes #550, fixes #530

And build for GOOS=darwin and GOARCH=arm

With this change, make should build the scope container on a correctly configured Mac, using Docker Machine.

[tomwilkie]

Tests temporarily turn off FDP due to weaveworks/weave#1577 (also the reason master is broken)

[peterbourgon]

ugh ~/src/github.com/weaveworks/scope (build-in-container) make
docker run -ti --rm -v /Users/peter/src:/go/src -e GOARCH -e GOOS weaveworks/scope-backend-build /build.bash
Unable to find image 'weaveworks/scope-backend-build:latest' locally
Pulling repository docker.io/weaveworks/scope-backend-build
Error: image weaveworks/scope-backend-build:latest not found
make: *** [backend] Error 1

Update: make clean isn't removing the .uptodate files...

[tomwilkie]

Ah good catch. Thanks, will fix.

[tomwilkie]

@peterbourgon PTAL

[tomwilkie]

@paulbellamy we've also switched out the ca-certificates for https://github.com/certifi/gocertifi as building on a Mac was giving this error:

make: *** No rule to make target `/etc/ssl/certs/ca-certificates.crt', needed by `docker/ca-certificates.crt'.  Stop.

Would you mind giving that a review?

[peterbourgon]

Currently broken due to that k8s import problem so my testing ability is compromised but LGTM.

[tomwilkie]

Thanks @peterbourgon; if you test #584 that includes all the changes from this PR and shouldn't build fine.

[tomwilkie]

Actually going to close this in favour of #584