Include the ability to utilize Hazelcast's SPI discovery in Confluence Data Center

Enterprise customers using Red Hat OpenShift and Kubernetes want the ability to dockerize Confluence Data Center nodes for quick and easy deployment. This would also benefit client running Confluence Data Center in AWS that wish to automate deployment (outside of using the AWS quick-start CloudFormation templates) and thus need to define static IP's in the confluence.cfg.xml config.

Due to the way this cloud works and/or security restrictions, they need the ability to use the Hazelcast SPI discovery instead of Multicast or Unicast.

Hazelcast 3.6+ is required to do this, but 3.8+ is preferred. Currently we use the following versions:

• Confluence 5.10.8 uses Hazelcast 3.4.2
• Confluence 6.0 through 6.6.5 uses Hazelcast 3.5.2
• Confluence 6.6.6+ uses Hazelcast 3.8.6: CONFSERVER-55867

Updated the above two lines to reflect changes in 6.6.x - Note that while Hazelcast was upgraded, this does not necessarily mean SPI is supported in Confluence yet.

Upgrading hazelcast to 3.8 would allow enterprise admins to more easily deploy Confluence Data Center nodes on the fly.