* 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>

- Created a Container options section in `docker/README.md`
- Add documentation for SOCAT_LINK
- Move CROND documentation to the new section

minor grammar fix

- Remove the known issue about `.dockerignore` being ignored during DockerHub automated build as this has been fixed
- Added a note on the fact that we currently do no support building the container on RPi1

- 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

- Add the crond init script for s6
- Add the RUN_CROND configuration variable to setup crond
- Crond will not be run by default (hence the `down` file in the service directory)
- `start.sh` check if RUN_CROND = "true" || "1" and remove this file to tell s6 to run the initscript
- Resolves #2597

- 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

- Resolve #1893
- Add syslogd to output sshd log on stdout (via `docker logs`)
- Enforce directory rights on `/data/git`, `/data/gogs` & `/data/ssh`
- Add `SOCAT_LINK` environment variable to prevent the creation of scout links when they are not needed (see #1815)

- Remove port 80 & 443 unused by the container
- Add port 3000 used by gogs application

- `start.sh` will now verify that the port is not already used by another service
- Resolve #1807
- Log when a service is created, or could not be created
- Keep track of which port is already used, including goes & sshd port

- ssh/setup: test directive now check if a file exist in key path instead of a folder
- ssh/setup script was hanging waiting for an input about rewriting the key
  as the test case was returning true, when it should have been false
  (check if file is a folder instead of a file)

- resolve #1765
- create link to old git repository path: `/home/git/gogs-repository`

- Volumed subfolder now created up in the ENTRYPOINT script, this way
  they are created before S6 even starts making VOLUME.
- The subfolder will be created during VOLUME creation too as ENTRYPOINT
  script will be run before /bin/true
- SSH Keys will now be created on a single key basis not replying on the
  existence of /data/ssh folder

- Fix s6 fifodir error on container restart
- Add .tags* to .gitignore (Atom auto ctags generation)

- Now using a setup script before starting the app. The separation of
the run script and the setup script will make service initialisation a
little bit clearer
- Now calling start.sh script as ENTRYPOINT and S6 as CMD. This way
when running the container with just a shell script, the start.sh
script will be launched before, making debugging easier
- Added note about `.dockerignore` ignored during Docker Hub Automated
Build

- 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