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.
Add docker_env group and make container_environment scripts group-readable
Update readme
Add USER, GROUP, UID, GID and SHELL to restricted env variables
my_init: runsvdir no longer redirects stderr to proctitle.

As described at http://smarden.org/runit/runsvdir.8.html passing a log
option to runsvdir causes stderr to be redirected to the proctitle.

That prevents stderr from reaching docker logs, which is a big problem.
Merge pull request #94 from pda/stderr-not-proctitle

my_init: runsvdir no longer redirects stderr to proctitle.
Merge pull request #84 from imanel/patch-1

Preserve ENV variables for SSH client
Update documentation
Change break to continue
Merge pull request #86 from imanel/patch-2

Don't write HOME env variable
Fixed typo.
Merge pull request #98 from bfitzsimmons/patch-1

Fixed typo.
Merge remote-tracking branch 'upstream/master' into feature-merge-upstream