Refactor and improve docker image downloading

Issue-ID: OOM-1803

Change-Id: I4e648d49835faa60165725d1ca4ec22ba1e3e12b
Signed-off-by: Milan Verespej <m.verespej@partner.samsung.com>
diff --git a/build/download/downloader.py b/build/download/downloader.py
index b8e9ed5..6440330 100644
--- a/build/download/downloader.py
+++ b/build/download/downloader.py
@@ -101,7 +101,10 @@
         """
         for item in self._merged_lists():
             if item not in self._missing:
-                log.info('File or directory present: {}'.format(item))
+                if type(self).__name__ == 'DockerDownloader':
+                    log.info('Docker image present: {}'.format(item))
+                else:
+                    log.info('File or directory present: {}'.format(item))
 
     def _merged_lists(self):
         """