* docker: update build script to use glide + make

- docker/build.sh will now use glide to fetch dependencies
- glide is built from source to keep compatibility with arm
  (no pre-prebuilt binary for arm)
- docker/build.sh will also now use the provided Makefile
  It will generate an error when trying to get git build has as we do
  not ship the 88mo .git directory during the build (should not cause
  any problem as the variable it sets was not set previously)

* docker: fix docker arm build

- drop gosu version back to 1.7 as gosu binary for armhf is broken
- see tianon/gosu#19

* docker: update gosu to 1.9

Signed-off-by: Jean-Philippe Roemer <jp@roemer.im>

- Upgrade of gosu to v1.7
- Change in docker/build.sh to use `--no-cache` to prevent APKINDEX creation when installing dev dependencies
- Manual upgrade of Alpine on Raspberry Pi when building to make sure the environment is the same as the standard Dockerfile

- Dockerfile now uses alpine:3.3 as base
- Dockerfile.rpi now uses v3.3/community repository without pinning
- Go package is no longer fetched using repository pinning
- Fixes problem while using repository pinning & virtual package at the same time

- Add nsswitch.conf to configure LibC Name Service inside the container
- Change my email in the Dockerfile
- Update build script to install software as a `build-deps` virtual package so that adding a package to it will be automatically	removed at the end of the build script

- Removed unnecessary variables
- Fixed symbolic links creation
- Fixed enter point
- Less intermediate containers

- VOLUME for ‘/data’
- Usage of S6 as PID 1 Process
- Usage of ‘socat’ so linked container (like databases) are binded to
localhost
- OpenSSH, Socat Link and Gogs are supervised using S6
- Size of container reduced to ~75Mo