Fix error with byte values in EXIF plugin.

Sometimes an EXIF tag contains raw bytes rather than an EXIFClass object.
Return the raw bytes as a string.

Change-Id: I7a0b1a9ba4e8e810093ab6030bcdca6adcee523b

python_nemesis/plugins/exif.py.plugin

@@ -43,5 +43,8 @@ class NemesisPlugin(object):
 
         ret_tags = {}
         for k, v in tags.items():
-            ret_tags[k] = v.printable
+            try:
+                ret_tags[k] = v.printable
+            except AttributeError:
+                ret_tags[k] = str(v)
         return ret_tags