esx: Fix memory leak

Variable def going out of scope leaks the storage def.source.hosts points to.

(cherry picked from commit d76267b2e4fb7a2388625b7cd4037d7b69db23d9)

src/esx/esx_storage_backend_vmfs.c

@@ -513,6 +513,7 @@ esxStoragePoolGetXMLDesc(virStoragePoolPtr pool, unsigned int flags)
     xml = virStoragePoolDefFormat(&def);
 
  cleanup:
+    VIR_FREE(def.source.hosts);
     esxVI_String_Free(&propertyNameList);
     esxVI_ObjectContent_Free(&datastore);
     esxVI_DatastoreHostMount_Free(&hostMount);