Use correct templates based on Elasticsearch versions

[suyograo]

ES 5.0 has numerous mapping changes as described here #386. Much effort has been put into making this a backward compatible change recently, but we'd still like users to migrate to the new mapping settings and not carry the old cruft around.

As such, we should:

• Ship both ES 2.x (old) and ES 5.0 (new) templates
• Enhance this plugin to detect if ES 5.0 is running (when the first attempt to upload template is made), and if so, use the 5.0 template version. If ES version 2.x is running, use the other template.

Note: We should do this only when default template is used and the existing template* configs should apply to both the versions

We may need to introduce a new config option to select different paths for 5.0 and 2.x templates on disk.

[pickypg]

I came back to this issue to double check that this part was here:

We should do this only when default template is used.

I just wanted to call it out for whoever implements it because otherwise it will break some things. :)

[suyograo]

Thanks @pickypg . Made it stick out :)

[tsg]

What does "force upgrade" mean? Overwrite it?

[suyograo]

@tsg when I mean't force upgrade, I actually meant forcing users to upgrade to a 5.0 template if they are running against ES 5.0. If they already have a logstash template, we wouldn't overwrite it.

[acchen97]

After discussion with @suyograo and @jordansissel we plan to backport this logic for 2.4 as well. Therefore, both LS 2.4 and 5.0 will have compatible default templates with both ES 2.x and 5.0.

[suyograo]

@jsvd moving this to @purbon

[suyograo]

@jsvd will start on this.

For ref: beats did something similar as well: elastic/beats#1993

[suyograo]

Fixed in #455