ArangoDB: fixed driver lifecycle #296
                
     Merged
            
            
          
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Changes
This PR fixes the shutdown of ArangoDB driver instances, delegating this responsibility to
ArangoDBDocumentManagerandArangoDBBucketManager.It changes the current behavior in the following way:
ArangoDBDocumentManagerandArangoDBBucketManagerhas its own ArangoDB driver instanceArangoDBDocumentManagerandArangoDBBucketManagerare responsible to shutdown their own driver instancesCleanup of ArangoDB sync builder (
ArangoDBBuilderSync).