Disable the unique_subject requirement

[stefanor]

Description

This allows more than one key with the same CN to exist in the CA's database. Which is useful for renewal, as it's the only mode of renewal supported by easy-rsa.

Issues Resolved

• Not filed: Unable to create a new client with the same CN as a previous client. E.g. for renewal.

Check List

• [x] All tests pass. See https://github.com/chef-cookbooks/community_cookbook_documentation/blob/master/TESTING.MD
• [x] New functionality includes testing.
• [x] New functionality has been documented in the README if applicable

[stefanor]

Tests are passing everywhere they do on master.

[stefanor]

Rebased on master.