Update verification for PLDM bios vs BMC time
Update verification for PLDM bios vs BMC time

Changes:
      - Add a new keyword to get BMC current date and time
      - update test code logic to do comparison

Tested:
      Ran test suite pldm/test_pldm_bios.robot

Change-Id: I246a775a4629f40e54ffcd91ebe92ff68d8be474
Signed-off-by: George Keishing <bef0a9ecac45fb57611777c8270153994e13fd2e@in.ibm.com>

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