Ubiquiti removed keytool (and java) from recent releases of Unifi OS. This moves from keytool to openssl's native pkcs12.
Tested on Unifi Dream Machine which runs Unifi OS and a built-in Unifi controller.
Also added backup of existing files prior to change in case anything goes wrong, and update system configuration with compatible ciphers.
This reverts commit 9a27b389765ac6d7a256333e9e1f6fe3c4b92e08.
Turns out, the Cloud Manager is not backward compatible, nor is the
Classic Manager forward compatible.
Linode API has made breaking changes that are resolved by this
update. No user action is required.
Additionally, related README.md entry updated to include new cloud
manager interface.
