Disable Nuxeo Stream when nuxeo.stream.audit.enabled is set to false

Steps to reproduce:

1. set these properties

   elasticsearch.enabled=false
   audit.elasticsearch.enabled=false
   nuxeo.stream.audit.enabled=false
   

2. start Nuxeo
3. observe the following errors in the logs

   2019-04-23T15:31:07,151 ERROR [ComputationRunner] bulkIndex: Exception in processLoop: null
   java.lang.NullPointerException: null
   	at org.nuxeo.elasticsearch.ElasticSearchComponent.getClient(ElasticSearchComponent.java:244) ~[nuxeo-elasticsearch-core-10.10-HF03.jar:?]
   	at org.nuxeo.elasticsearch.bulk.BulkIndexComputation.getESClient(BulkIndexComputation.java:148) ~[nuxeo-elasticsearch-core-10.10-HF03.jar:?]
   	at org.nuxeo.elasticsearch.bulk.BulkIndexComputation.init(BulkIndexComputation.java:96) ~[nuxeo-elasticsearch-core-10.10-HF03.jar:?]
   	at org.nuxeo.lib.stream.computation.log.ComputationRunner.run(ComputationRunner.java:156) [nuxeo-stream-10.10-HF02.jar:?]
   	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_151]
   	at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_151]
   	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_151]
   	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_151]
   	at java.lang.Thread.run(Thread.java:748) [?:1.8.0_151]
   2019-04-23T15:31:07,147 ERROR [ComputationRunner] bulkIndex: Exception in processLoop: null
   java.lang.NullPointerException: null
   	at org.nuxeo.elasticsearch.ElasticSearchComponent.getClient(ElasticSearchComponent.java:244) ~[nuxeo-elasticsearch-core-10.10-HF03.jar:?]
   	at org.nuxeo.elasticsearch.bulk.BulkIndexComputation.getESClient(BulkIndexComputation.java:148) ~[nuxeo-elasticsearch-core-10.10-HF03.jar:?]
   	at org.nuxeo.elasticsearch.bulk.BulkIndexComputation.init(BulkIndexComputation.java:96) ~[nuxeo-elasticsearch-core-10.10-HF03.jar:?]
   	at org.nuxeo.lib.stream.computation.log.ComputationRunner.run(ComputationRunner.java:156) [nuxeo-stream-10.10-HF02.jar:?]
   	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_151]
   	at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_151]
   	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_151]
   	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_151]
   	at java.lang.Thread.run(Thread.java:748) [?:1.8.0_151]
   

By investigating a little, I noticed that thread pools are started for many other computations (AuditLogWriter, CSVExport, etc) but do not produce errors.

I tried to disable to contributions in templates/common-base/nxserver/config/stream-config.xml.nxftl and to nuxeo-stream.jar, but none of these workarounds work.