Flush stream after writing service messages

sys.stdout is buffered by default if redirected to a file.
This may causes automated installation to appear hung.
Flush the stream so that messages are written immediately.

ipaserver/install/service.py

@@ -55,6 +55,7 @@ def print_msg(message, output_fd=sys.stdout):
     root_logger.debug(message)
     output_fd.write(message)
     output_fd.write("\n")
+    output_fd.flush()
 
 
 class Service(object):