Do not remove the `/usr/local/elasticsearch` directory when it's a symlink.

This means it was created by Ark, not by Chef when creating the user.

h/t: @avishai-ish-shalom

Related: #104
Do not run "ark" when the required version is already installed

This prevents:

* Downloading the already downloaded file on each Chef run
* Restarting the Elasticsearch service on each Chef run

Closes #104

Related: bryanwb/chef-ark#40