Fix bug for PNOR code update test cases
Fix bug for PNOR code update test cases

- When uploading the alternate image during PNOR code update
  tests, we need to make sure the alternate image is not
  already on the BMC.

Change-Id: Ibc609dca83c284989b3c5fbb0a1cffb036a62772
Signed-off-by: Charles Paul Hofer <08feea5166a3d3d271f0e9271c1c675fb81e7eda@ibm.com>

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