Preserve ENV variables for SSH client

Currently when you ssh to host you will not see ENV variables set. This was mentioned earlier in #54 and solution is tested.

Additional rationale: currently you can't see docker link ENV variables inside ssh, so you need to load this file every time you connect to container. I would say that expected behavior is to preserve them in services that are provided at default (cron/ssh)
Don't write HOME env variable

Loading HOME variable breaks multi-user container (i.e. logging as postgres user) if you try to load variables via `/etc/container_environment.sh`.
Make container_envoriments.sh and .json readable by other users

Prevents bug when loading env variables on non-root user login.
Missing target of chown
needed for insecure key usage

`chmod 600` is for the benefit of ssh client, which will otherwise spew:

```
chmod 600 image/insecure_key.pub
SSHing into 172.17.0.2
Warning: Permanently added '172.17.0.2' (ECDSA) to the list of known hosts.
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@         WARNING: UNPROTECTED PRIVATE KEY FILE!          @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
Permissions 0664 for 'image/insecure_key' are too open.
It is required that your private key files are NOT accessible by others.
This private key will be ignored.
bad permissions: ignore key: image/insecure_key
```

As you can see though, the wrong file is `chmod`'ed -- it's the private key that SSH will insist should be protected with a more restrictive mode.

After this, `CMD ["/sbin/my_init", "--enable-insecure-key"]` works as expected.
Create CONTRIBUTING.md
Update CONTRIBUTING.md

Fix link
Use Go template instead of grep to extract container IP address
Bump version to 0.9.11
Install add-apt-repository.

Closes GH-74.
Merge pull request #90 from yebyen/patch-1

needed for insecure key usage
Merge pull request #88 from jeckhart/fix-syslogng-runit-run

Missing target of chown in syslog-ng runit run file
Update Changelog
Fixed various process waiting issues in `my_init`.

Closes GH-27. Closes GH-82. Closes GH-83.
Thanks to André Luiz dos Santos and Paul Annesley.
Merge pull request #93 from qerub/ipaddress

Use Go template instead of grep to extract container IP address
Introduce the `docker-bash` tool.

This is a shortcut tool for logging into a container using SSH. Usage: `docker-bash <CONTAINER_ID>`.
Fix an anchor in the README
Add docker_env group and make container_environment scripts group-readable
Update readme
Add USER, GROUP, UID, GID and SHELL to restricted env variables