feat(docker::run): add the enable param

[reppard]

Here is a possible answer to #308. All tests passing with the exception of one unrelated beaker test. I confirmed that this test is failing sans this code change.

spec/acceptance/docker_spec.rb:114 # docker registry should be able to login to the registry

Example:

docker::run { 'seagull':
  image         => 'tobegit3hub/seagull:1.3.0',
  ports         => ['10086:10086'],
  volumes       => ['/var/run/docker.sock:/var/run/docker.sock'],
  enable        => true,
  running       => false,
  pull_on_start => true,
  require       => Class['docker'],
}

This would allow us to enable services without starting the service or pulling the images down until a reboot or the services are manually triggered. This is useful for baking things like Vagrant boxes and AMIs.

Whether or not this can be merged, feedback would be greatly appreciated! I would be happy to make suggested changes and update the PR so we can get this functionality added to the module.

Thanks for the great work.

• Reppard