Upgraded from 5.16.1 to 6.0.0-EAP1, using the installation wizard to perform the upgrade.

Now Elastisearch fails with the following stack trace;

```
[2019-02-12T19:06:24,484][WARN ][o.e.b.ElasticsearchUncaughtExceptionHandler] [bitbucket_bundled]uncaught exception in thread [main]
org.elasticsearch.bootstrap.StartupException: java.lang.IllegalArgumentException: unknown setting [path.conf] please check that any required plugins are installed, or check the breaking changes documentation for removed settings
at org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:140) ~[elasticsearch-6.5.3.jar:6.5.3]
at org.elasticsearch.bootstrap.Elasticsearch.execute(Elasticsearch.java:127) ~[elasticsearch-6.5.3.jar:6.5.3]
at org.elasticsearch.cli.EnvironmentAwareCommand.execute(EnvironmentAwareCommand.java:86) ~[elasticsearch-6.5.3.jar:6.5.3]
at org.elasticsearch.cli.Command.mainWithoutErrorHandling(Command.java:124) ~[elasticsearch-cli-6.5.3.jar:6.5.3]
at org.elasticsearch.cli.Command.main(Command.java:90) ~[elasticsearch-cli-6.5.3.jar:6.5.3]
at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:93) ~[elasticsearch-6.5.3.jar:6.5.3]
at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:86) ~[elasticsearch-6.5.3.jar:6.5.3]
Caused by: java.lang.IllegalArgumentException: unknown setting [path.conf] please check that any required plugins are installed, or check the breaking changes documentation for removed settings
at org.elasticsearch.common.settings.AbstractScopedSettings.validate(AbstractScopedSettings.java:476) ~[elasticsearch-6.5.3.jar:6.5.3]
at org.elasticsearch.common.settings.AbstractScopedSettings.validate(AbstractScopedSettings.java:421) ~[elasticsearch-6.5.3.jar:6.5.3]
at org.elasticsearch.common.settings.AbstractScopedSettings.validate(AbstractScopedSettings.java:392) ~[elasticsearch-6.5.3.jar:6.5.3]
at org.elasticsearch.common.settings.AbstractScopedSettings.validate(AbstractScopedSettings.java:363) ~[elasticsearch-6.5.3.jar:6.5.3]
at org.elasticsearch.common.settings.SettingsModule.<init>(SettingsModule.java:148) ~[elasticsearch-6.5.3.jar:6.5.3]
at org.elasticsearch.node.Node.<init>(Node.java:373) ~[elasticsearch-6.5.3.jar:6.5.3]
at org.elasticsearch.node.Node.<init>(Node.java:265) ~[elasticsearch-6.5.3.jar:6.5.3]
at org.elasticsearch.bootstrap.Bootstrap$5.<init>(Bootstrap.java:212) ~[elasticsearch-6.5.3.jar:6.5.3]
at org.elasticsearch.bootstrap.Bootstrap.setup(Bootstrap.java:212) ~[elasticsearch-6.5.3.jar:6.5.3]
at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:333) ~[elasticsearch-6.5.3.jar:6.5.3]
at org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:136) ~[elasticsearch-6.5.3.jar:6.5.3]
... 6 more
```

Atlassian-bitbucket.log contains the following;
```
2019-02-12 19:07:10,386 INFO [Caesium-1-1] c.a.b.i.s.i.jobs.StartupChecksJob Running startup jobs for search
2019-02-12 19:07:12,421 WARN [Caesium-1-1] c.a.b.i.s.i.IndexingSynchronizationService Unable to establish a connection to Elasticsearch during index synchronisation.
2019-02-12 19:07:12,421 WARN [Caesium-1-1] c.a.b.i.s.c.cluster.ClusterJobRunner Job execution failed. Rescheduling. Job key: com.atlassian.bitbucket.internal.search.indexing.jobs.StartupChecksJob Job id: a736caa6-8747-47aa-9076-a3d92447f41d
```

I have attached the bitbucket_search log

otherwise all logs are unremarkable.

Please let me know if there is anything else I can provide you.