Set system, chassis, and bmc as global variables

Changes:
  - Add SYSTEM_ID as a global variable and set to default value system
  - Replace redfish/v1/Systems/system to redfish/v1/Systems/SYSTEM_ID
  - Replace redfish/v1/Chassis/chassis to redfish/v1/Chassis/CHASSIS_ID
  - Replace redfish/v1/Managers/bmc to redfish/v1/Managers/MANAGER_ID

Tested:
  - Tested on sandbox with the changes with sample test run with
    sample test ID runs
    1. without SYSTEM_ID provided
    2. with -v SYSTEM_ID:system1
    3. with export SYSTEM_ID=""
    3. with export SYSTEM_ID="system2"

Change-Id: Ifc412b20038cef1eba632caaa6c300be328259bd
Signed-off-by: Wilson Suen <wilsons@supermicro.com>
Signed-off-by: George Keishing <gkeishin@in.ibm.com>
diff --git a/openpower/test_timed_power_on.robot b/openpower/test_timed_power_on.robot
index 0fe7517..2f24511 100644
--- a/openpower/test_timed_power_on.robot
+++ b/openpower/test_timed_power_on.robot
@@ -119,7 +119,7 @@
     # Description of argument(s):
     # power_policy_mode           BIOS attribute value. E.g. "Stay On", "Automatic".
 
-    Redfish.Patch  /redfish/v1/Systems/system/Bios/Settings
+    Redfish.Patch  /redfish/v1/Systems/${SYSTEM_ID}/Bios/Settings
     ...  body={"Attributes":{"pvm_system_power_off_policy": "${power_policy_mode}"}}
     ...  valid_status_codes=[${HTTP_OK}]