Don't start embedded elastic when running unit test on remote ES cluster

Since NXP-28131 we can run unit test against a remote elastic.
using

-Dnuxeo.test.elasticsearch.addressList=http://localhost:9200

The elastic client connects to the specified cluster, nevertheless an embedded node is started.

How to check:
1. make sure you don't have any elasticsearch server running
2. run

cd modules/platform/nuxeo-elasticsearch/nuxeo-elasticsearch-core
mvn -nsu clean test -Dtest=org.nuxeo.elasticsearch.test.scroll.TestElasticSearchScroll  -Dnuxeo.test.elasticsearch.addressList=http://localhost:9200

The test pass instead of failing because an embedded node is started.
Note that if you have an elastic running on localhost:9200 prior to run the test, the test will use your elastic server as expected (the embeded server is started on another port).