Don't start scroller computation when stream processors are disabled

Since NXP-29361 (10.10 HF30) it is possible to disable processors on specific nodes using nuxeo.stream.processing.enabled=false.
In this case all processors including bulk action processors are not started (there are any consumer threads on Kafka) except for the scroller computation.

We don't want to have this scroller computation started.

In 10.10 the bulk service is started programmatically (in master it is done using a normal contribution NXP-28357) this explains why this special computation is started anyway and why this is specific to 10.10.