Support for missing elasticsearch options

[mistic]

Since Kibana 6.6 the option elasticsearch.url is not used anymore and instead we use elasticsearch.hosts.

For now I also left the old option enabled here.

Aside from this main added option, other elasticsearch options were also added:

elasticsearch.sniffInterval
elasticsearch.sniffOnConnectionFault
elasticsearch.sniffOnStart

This should be backported to 6.6, 6.x and 6.x-i18n branch too.

Closes #120

[joshdover]

@mistic It looks like the default kibana.yml that gets copied in also has elasticsearch.url. I think we just need to make sure that gets updated in 7.0

[mistic]

@joshdover doesn't make sense to also apply it to 6.6.x and 6.7 as long as if someone wanna simply use elasticsearch.hosts it would fail?

[joshdover]

As long as elasticsearch.url takes precedence I think that's fine. If not, then the user may have a problem if the default yaml has elasticsearch.hosts set to localhost:9200 and they provide the ELASTICSEARCH_URL env var, we need to make sure it doesn't try to connect to localhost:9200.

[mistic]

@joshdover I'm just thinking about clients who will install Kibana for example for the first time in 6.6.0 or in 6.6.1.

6.6.0:

They will have the docs reverted but in case they just look to the kibana.yml file they will find the elasticsearch.hosts option which can let them define ELASTICSEARCH_HOSTS option for the docker image.

6.6.1:

They will find the same thing into the config and also the the docs updated, now pointing to elasticsearch.hosts.

Don't u think it is still a good idea to backport this to 6.6 and 6.x?

[tylersmalley]

Let's also make sure we have:

elasticsearch.sniffOnStart
elasticsearch.sniffInterval
elasticsearch.sniffOnConnectionFault

[mistic]

@tylersmalley thanks for letting me know about those ones too! They were also added.