Refactor handling of SMAP instrument information

Current SMAP instrument metadata is not compatible with the expected
UMM-G mappings. This results in CMR flagging the UMM-G metadata as
invalid. To work around this issue, instrument information is not
carried over to UMM-G. This commit is a cleanup of the first pass
on addressing this issue. Handling of instrument information is now
conditional based on whether any useful data was extracted from the
source metadata so that the functionality remains available should
future SMAP metadata adhere to published UMM-G mappings.

src/main/java/gov/nasa/cumulus/metadata/aggregator/MetadataFilesToEcho.java

@@ -838,12 +838,22 @@ private void readIsoSmapMetadataFile(String s3Location, Document doc, XPath xpat
 
         Source source = new Source();
         source.setSourceShortName(xpath.evaluate(IsoSmapXPath.PLATFORM, doc));
+		Sensor sensor = new Sensor();
+		sensor.setSensorShortName(xpath.evaluate(IsoSmapXPath.INSTRUMENT, doc));
 
         DatasetSource datasetSource = new DatasetSource();
         DatasetSource.DatasetSourcePK datasetSourcePK = new DatasetSource.DatasetSourcePK();
         datasetSourcePK.setSource(source);
         datasetSource.setDatasetSourcePK(datasetSourcePK);
 
+		datasetSourcePK.setSource(source);
+
+	    if (!sensor.getSensorShortName().trim().isEmpty()) {
+			datasetSourcePK.setSensor(sensor);
+		}
+
+		datasetSource.setDatasetSourcePK(datasetSourcePK);
+
         dataset.add(datasetSource);
 
         NodeList inputGranules = (NodeList) xpath.evaluate(IsoSmapXPath.GRANULE_INPUT, doc, XPathConstants.NODESET);

src/main/java/gov/nasa/cumulus/metadata/aggregator/UMMGranuleFile.java

@@ -883,11 +883,13 @@ private JSONArray exportPlatform() {
             JSONObject platform = new JSONObject();
             platform.put("ShortName", datasetSource.getDatasetSourcePK().getSource().getSourceShortName());
 
-            JSONArray instruments = new JSONArray();
-            JSONObject instrument = new JSONObject();
-            instrument.put("ShortName", datasetSource.getDatasetSourcePK().getSensor().getSensorShortName());
-            instruments.add(instrument);
-            platform.put("Instruments", instruments);
+            if (!datasetSource.getDatasetSourcePK().getSensor().getSensorShortName().trim().isEmpty()) {
+                JSONArray instruments = new JSONArray();
+                JSONObject instrument = new JSONObject();
+                instrument.put("ShortName", datasetSource.getDatasetSourcePK().getSensor().getSensorShortName());
+                instruments.add(instrument);
+                platform.put("Instruments", instruments);
+            }
 
             platforms.add(platform);
         }