The role makes use of some variables from common_vars (notably COMMON_*_DIR), so
it should depend on the "common" role.  With this change applied, it's possible
to run the elasticsearch role using the run_role.yml playbook, which is
sometimes convenient.

It pulls the setting into the comment above it if you do that.

Until now it's only been used for clustered deployment,
but it works fine in single-instance mode, too.

This solves the problem for installations failing with this message:
"msg: Failed to validate the SSL certificate for download.elasticsearch.org:443. Use validate_certs=no or make sure your managed systems have a valid CA certificate installed. Paths checked for this platform: /etc/ssl/certs, /etc/pki/ca-trust/extracted/pem, /etc/pki/tls/certs, /usr/share/ca-certificates/cacert.org, /etc/ansible"

I recently had a build where elasticsearch hadn't auto started so
I added that check here.