Improved error output of obmc_ser_num.
Improved error output of obmc_ser_num.

Change-Id: Ic456688f74184a6af92af073f08cbb9b7eea4672
Signed-off-by: Michael Walsh <10404802c7de463f402c4a18638106ca1b12ef61@us.ibm.com>

openbmc/openbmc-test-automation,openbmc/openbmc-test-automation