Module should have option to manage DOCKER_HOST environment variable

[mlehner616]

When specifying a tcp_bind, in order for this to actually be usable the DOCKER_HOST environment variable needs to be populated with the tcp_bind value:

Proposed solution:

if $tcp_bind {
  file { '/etc/profile.d/docker-host.sh': 
    ensure  => file,
    content => "export DOCKER_HOST=${tcp_bind}"
  }
}

[garethr]

I think the correct way of setting this is in https://github.com/garethr/garethr-docker/blob/master/templates/etc/default/docker.erb, rather than doing something at the profile level. I'd definitely be open to a pull request for this, good idea.

[garethr]

As of #171 you can now pass an array of shell values to the module, which should support this usecase.