Change to ArgumentDefaultsHelpFormatter.

Changed from this:
formatter_class=argparse.RawTextHelpFormatter

To this:
formatter_class=argparse.ArgumentDefaultsHelpFormatter

This greatly improves the formatting of the help text.

Change-Id: Ie3ad6afe0b3cda50e1b032c37a20ff22733de9bd
Signed-off-by: Michael Walsh <micwalsh@us.ibm.com>
diff --git a/bin/obmc_ser_num b/bin/obmc_ser_num
index 4f7958b..8cd05ad 100755
--- a/bin/obmc_ser_num
+++ b/bin/obmc_ser_num
@@ -26,7 +26,7 @@
     description="%(prog)s will get the system serial number from an OBMC" +
                 " machine and print it to stdout as follows:\n\n" +
                 "mch_ser_num:<ser num>",
-    formatter_class=argparse.RawTextHelpFormatter,
+    formatter_class=argparse.ArgumentDefaultsHelpFormatter,
     prefix_chars='-+')
 
 parser.add_argument(