Term Vector settings should be treated like flags without propergation

today if a specific feature is disabled for term vectors with something
like 'store_term_vector_positions = false' term vectors might be disabeled
alltogether even if 'store_term_vectors=true' in the mapping. This depends on the
order of the values in the mapping since the more specific one might override
the less specific on.

Closes elastic#4582

src/main/java/org/elasticsearch/index/mapper/core/AbstractFieldMapper.java

@@ -187,24 +187,32 @@ protected T store(boolean store) {
         }
 
         protected T storeTermVectors(boolean termVectors) {
-            this.fieldType.setStoreTermVectors(termVectors);
+            if (termVectors) {
+                this.fieldType.setStoreTermVectors(termVectors);
+            } // don't set it to false, it is default and might be flipped by a more specific option
             return builder;
         }
 
         protected T storeTermVectorOffsets(boolean termVectorOffsets) {
-            this.fieldType.setStoreTermVectors(termVectorOffsets);
+            if (termVectorOffsets) {
+                this.fieldType.setStoreTermVectors(termVectorOffsets);
+            }
             this.fieldType.setStoreTermVectorOffsets(termVectorOffsets);
             return builder;
         }
 
         protected T storeTermVectorPositions(boolean termVectorPositions) {
-            this.fieldType.setStoreTermVectors(termVectorPositions);
+            if (termVectorPositions) {
+                this.fieldType.setStoreTermVectors(termVectorPositions);
+            }
             this.fieldType.setStoreTermVectorPositions(termVectorPositions);
             return builder;
         }
 
         protected T storeTermVectorPayloads(boolean termVectorPayloads) {
-            this.fieldType.setStoreTermVectors(termVectorPayloads);
+            if (termVectorPayloads) {
+                this.fieldType.setStoreTermVectors(termVectorPayloads);
+            }
             this.fieldType.setStoreTermVectorPayloads(termVectorPayloads);
             return builder;
         }