Change the name of the first background image

Which image we pick doesn't matter, but our logic only looks for
the first one, it doesn't loop through all possible matches.

check-persona-url.py

@@ -64,7 +64,7 @@ def get_static_png(persona_org):
     print '  ERROR: Could not find background-image url in /%s' % css_file
     return
   path = match.group(1)
-  if not path.endswith('/common/i/grain.png'):
+  if not path.endswith('/common/i/closex.png'):
     print '  ERROR: Found background-image url but it is the wrong one: %s' % path
     return
   return path