[elixir] extracting env information from docker-machine via command execution/parsing

docker_machine.ex

```
defmodule DockerMachine do 
  def get_env() do
    case System.cmd("docker-machine", ["env","local"]) do
      {output,0} -> {
                    :success, output |> 
                    String.split("\n") |> 
                    Enum.filter(fn x -> x =~ "export DOCKER" end) |>
                    Enum.map( fn l ->  
                      String.replace(l, ~r/export (.*)/,"\\1") |> 
                      String.replace(~r/\"/,"") |> 
                      String.split("=") |> 
                      List.to_tuple end)|>
                    Enum.map(
                     fn 
                       {"DOCKER_TLS_VERIFY", docker_tls_verify} ->    {:docker_tls_verify, docker_tls_verify}
                       {"DOCKER_HOST", docker_host} ->                {:docker_host, docker_host} 
                       {"DOCKER_CERT_PATH", docker_cert_path} ->      {:docker_cert_path, docker_cert_path} 
                       {"DOCKER_MACHINE_NAME",docker_machine_name} -> {:docker_machine_name,docker_machine_name} 
                       other -> {:error, other}
                     end 
                    )
                   }
      {output,number} -> {:error,output,number}
      other -> {:error,other}
    end
  end
end
```

iex(11)> {:success, keylist} = Docker.DockerMachine.get_env
{:success,
 [docker_tls_verify: "1", docker_host: "tcp://192.168.103.138:2376",
  docker_cert_path: "/Users/bryanhunt/.docker/machine/machines/local",
  docker_machine_name: "local"]}

iex(13)> Map.new(keylist)
%{docker_cert_path: "/Users/binarytemple/.docker/machine/machines/local",
  docker_host: "tcp://192.168.103.138:2376", docker_machine_name: "local",
  docker_tls_verify: "1"}

Hoping to use it in this way ( config/dev.exs )

use Mix.Config
{:success, keylist} = DockerMachine.get_env
m = Map.new(keylist)

config :docker,
        base_url: m[:docker_host],
        ssl_options: [
          {:ca_file,   m[:docker_cert_path] <> "/docker.crt"},
          {:cert_file, m[:docker_cert_path] <> "/docker.crt"},
          {:key_file,  m[:docker_cert_path] <> "/ca.crt"},
        ],  
        machine_name: m[:docker_machine_name]