Petascope_Log warn instead of throwing exception if metadata is malformed

[Bang Pham Huu]

e.g: add metadata as array as the example below in ingredient file, then request DescribeCoverage, it will throw an exception.

Caused by: com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of petascope.core.gml.metadata.model.LocalMetadata: no String-argument c

   "global": {
            "resolution": "'1'",
            "slices": []
          }

Hence, to make request still can return result of existing coverages, it will log it with warn level instead.