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/ipmi/test_ipmi_general.robot b/ipmi/test_ipmi_general.robot
index 0eba9ab..4f9fa3b 100644
--- a/ipmi/test_ipmi_general.robot
+++ b/ipmi/test_ipmi_general.robot
@@ -435,6 +435,6 @@
     # power_cap_value    Power cap value which need to be set.
 
     # Set power cap value based on argument.
-    Redfish.Patch  /redfish/v1/Chassis/chassis/EnvironmentMetrics
+    Redfish.Patch  /redfish/v1/Chassis/${CHASSIS_ID}/EnvironmentMetrics
     ...  body={"PowerLimitWatts":{"SetPoint": ${power_cap_value}}}
     ...  valid_status_codes=[${HTTP_OK}, ${HTTP_NO_CONTENT}]