XML Server configuration fetched instead of JSON expected in DynamicServerConfigurationService

[lbar]

In DynamicServerConfigurationService the server configuration is fetched by using Spring RestTemplate. In a complex Spring environment using XML and JSON HTTP mappers, the RestTemplate will accept first application/xml then application/json when expected object is of type String. This choice is perhaps not the most appropriate from Spring, but it should be managed inside DynamicServerConfigurationService.

A solution is to use Jackson instead of GSON, in order to fetch configuration by calling restTemplate.getForObject(url, JsonNode.class).

[lbar]

See #1489 for fix