Expire admin password using root privileged user

Tested:

       Ran successfully  redfish/update_service/
       test_redfish_bmc_code_update.robot

Change-Id: I6e80e07f34df754805627a35f6c4446d85bbbfc6
Signed-off-by: Sushil Singh <susilsi7@in.ibm.com>
diff --git a/lib/bmc_redfish_utils.robot b/lib/bmc_redfish_utils.robot
index 7a69863..fab151a 100644
--- a/lib/bmc_redfish_utils.robot
+++ b/lib/bmc_redfish_utils.robot
@@ -305,7 +305,7 @@
     # new_password    The new password to be used to update password.
 
     # Expire admin password using ssh.
-    Open Connection And Log In  ${username}  ${password}
+    Open Connection And Log In  ${OPENBMC_USERNAME}  ${OPENBMC_PASSWORD}
     ${output}  ${stderr}  ${rc}=  BMC Execute Command  passwd --expire ${username}
     Should Contain Any  ${output}  password expiry information changed
     ...  password changed