Junit tests in nuxeo-core-mongodb should not fail when there is no Mongo

Discovered while building nuxeo-core with no Mongo running on JenkinsX:

TestMongoDBKeyValueStore and TestSequenceGeneratorWithMongoDB fail with:

java.lang.AssertionError: invoke on features error [Holder [type=class org.nuxeo.runtime.test.runner.MDCFeature], Holder [type=class org.nuxeo.runtime.test.runner.ConditionalIgnoreRule$Feature], Holder [type=class org.nuxeo.runtime.test.runner.RandomBug$Feature], Holder [type=class org.nuxeo.runtime.test.runner.RuntimeFeature], Holder [type=class org.nuxeo.runtime.mongodb.MongoDBFeature]]

—

Suppressed: com.mongodb.MongoTimeoutException: Timed out after 30000 ms while waiting to connect. Client view of cluster state is {type=UNKNOWN, servers=[{address=localhost:27017, type=UNKNOWN, state=CONNECTING, exception=

Unknown macro: {com.mongodb.MongoSocketOpenException}

, caused by {java.net.ConnectException: Connection refused (Connection refused)}}]

See job at: http://jenkins.l2it.35.231.200.170.nip.io/job/nuxeo-sandbox/job/nuxeo/job/master/59/

Looks like these tests pass on QA because we always run Mongo on very slave