Security improvements for Kibana/Nginx

[jimmycuadra]

This branch includes one change and one addition related to security and Kibana's web server:

• Disallow the SSLv3 protocol which is vulnerable to POODLE. Update the allowed TLS cipher suite according to current best practices.

  Reference: https://raymii.org/s/tutorials/Strong_SSL_Security_On_nginx.html.

• Add a new attribute, ['elkstack']['config']['kibana']['prepare_ssl'] which allows users to disable the kibana_ssl recipe if they wish to configure this themselves (including providing their own certificate and private key). The default is true, meaning the behaivor stays as it is by default.

[jimmycuadra]

CI failure looks like a configuration problem... This passed kitchen test for me locally.

[martinb3]

@jimmycuadra Thanks for the contribution! CircleCI won't build branches owned by a non-project/non-approved owner, as it could potentially expose secrets. This is expected behavior. I've pushed a branch with your changes into the main git repo, so that they will be tested appropriately.

[martinb3]

Looks like this ended up choking on a current rubocop gem issue: rubocop/rubocop#2218

I've added ff15484 and it did pass in CircleCI after that, so I'm going to manually merge, and it will include your commits. Thank you for the contribution @jimmycuadra!

[jimmycuadra]

Thanks for merging! If you think of it, please leave a comment here when a new version is uploaded to the Supermarket so I can update my wrapper cookbook. :}

[martinb3]

@jimmycuadra No problem! I pushed 6.0.4 with your changes, so you should be all set to use Supermarket again.