rabbitmq-atp-update: Fixes "Failed to find required executable rabbitmq-plugins"

Without the `apt-get update`, the apt cache is out of date while attempting to install
rabbitmq. An older version from the Ubuntu repo is installed instead of the one from
the rabbit repository, which makes the role fail later on with:

```
TASK: [rabbitmq | install plugins] ********************************************
[...]
failed: [10.145.2.22] => {"failed": true, "item": ""}
msg: Failed to find required executable rabbitmq-plugins
```
java-link-var: Replace `java_link` var by `oraclejdk_link`

This variable doesn't seem to be defined anywhere, and (in v1.3?) ansible
complains about the missing value. Since there is a `oraclejdk_link` which
seem to correspond, replacing.
ssl-nginx: Add new LMS variant to serve SSL through nginx