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.
The dns_nederhost DNS API relies on the exact HTTP status code to be
returned (e.g. 204); however, the _get function always returns 200 for a
succesful call when using wget instead of curl. This patch fixes this by
using the _post function for all requests done by dns_nederhost.
