Gh-3303: No error reported when Gremlin endpoint fails #2599

Job	Run time
Check all modules are tested	6s
Build Javadoc	5m 4s
Check Copyright Headers	40s
Check Markdown Links	39s
Tests (ubuntu-latest, Core, :gaffer2,:core,:access,:cache,:common-util,:data,:exception,:graph,:o...	4m 17s
Tests (ubuntu-latest, Accumulo, :accumulo-store,:accumulo-rest)	28m 48s
Tests (ubuntu-latest, Federated-And-Map, :integration-test,:federated-store,:map-store,:map-rest,...	20m 22s
Tests (ubuntu-latest, REST, :rest-api,:common-rest,:spring-rest,:core-rest,:store-implementation,...	6m 53s
Tests (ubuntu-latest, Examples, :example,:basic,:basic-model,:basic-rest,:road-traffic,:road-traf...	3m 37s
Tests (ubuntu-latest, Big-Data-Libraries, :flink-library,:hdfs-library,:spark,:spark-library,:spa...	8m 20s
Tests (ubuntu-latest, Time-Library, :library,:time-library)	1m 19s
Tests (ubuntu-latest, Caches, :cache-library,:sketches-library,:bitmap-library,:hazelcast-cache-s...	2m 14s
Tests (ubuntu-latest, Tinkerpop, :tinkerpop)	5m 11s
Upload coverage to Codecov	10s
	1h 27m 40s

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