Add missing redfish.logout

Change-Id: I0ea4c8cc66d680966ce82510a88ca8c602df39fc
Signed-off-by: Sivas SRR <sivas.srr@in.ibm.com>
diff --git a/redfish/update_service/test_firmware_inventory.robot b/redfish/update_service/test_firmware_inventory.robot
index 5ca0965..0b0848f 100644
--- a/redfish/update_service/test_firmware_inventory.robot
+++ b/redfish/update_service/test_firmware_inventory.robot
@@ -80,3 +80,4 @@
     \  Should Be Equal As Strings  ${resp_resource.dict["Status"]["Health"]}  OK
     \  Should Be Equal As Strings  ${resp_resource.dict["Status"]["HealthRollup"]}  OK
     \  Should Be Equal As Strings  ${resp_resource.dict["Status"]["State"]}  Enabled
+    redfish.Logout