I think this line is the clue:
Caused by: java.lang.NoClassDefFoundError: org/elasticsearch/plugins/NetworkPlugin
There is an issue with dependencies (versions)
From here (ClassNotFoundException: org.elasticsearch.plugins.ActionPlugin · Issue #21172 · elastic/elasticsearch · GitHub) the suggested solution is adding something to your pom.xml properties section.
<elasticsearch.version>5.3.0</elasticsearch.version>
An alternative i found here ( spring - Elasticsearch TransportClient NetworkPlugin NoClassDefFoundError - Stack Overflow ) is putting the main elastic artifact in your pom.xml