Make rpm/deb packages more similar to Elasticsearch

[jordansissel]

Reference: https://www.elastic.co/guide/en/elasticsearch/reference/master/rpm.html#rpm-layout

We currently install to /opt, where Elasticsearch uses /usr, /var, et al. Let's move towards Elasticsearch's model.

Major task:

• Update rake artifact:rpm and deb tasks to use a file layout similar to Elasticsearch's See Feature/release packaging #5341
• Write tool for migrating stored plugin state to the new location.

Upgrade tooling needed. The following plugins store state somewhere by default. For rpm/deb, it will need to move to /var/lib/logstash/

• file
• s3
• jdbc

(please add other state-storing plugins to the above list)

[suyograo]

For these state file upgrades, we should start with an external script (bash, or ruby or whatever) which copies the state files from $OLD_HOME to new /var/lib.

Also need to add breaking changes doc (edited the issue)

[suyograo]

Done in #5341