Add IPMI_POWEROFF_WAIT_TIMEOUT varaible for user input

By default 3 minutes, however on a booted system with partition(s),
a soft power off can take longer. This give flexibility to override
the default and test can wait on user input.

Tested:
     robot -v OPENBMC_HOST:xx.xx.xx.xx -v IPMI_POWEROFF_WAIT_TIMEOUT:10
           --include Verify_Soft_Shutdown ipmi/test_ipmi_chassis.robot

Test Ipmi Chassis :: Module to test IPMI chassis functionality.       | PASS |
1 test, 1 passed, 0 failed

Change-Id: Ib82c854577509b24d02e9b92a443e6af6a69f5f2
Signed-off-by: George Keishing <gkeishin@in.ibm.com>
diff --git a/ipmi/test_ipmi_chassis.robot b/ipmi/test_ipmi_chassis.robot
index 28376fe..9383425 100644
--- a/ipmi/test_ipmi_chassis.robot
+++ b/ipmi/test_ipmi_chassis.robot
@@ -11,6 +11,10 @@
 Suite Teardown   Redfish.Logout
 Test Teardown    Test Teardown Execution
 
+*** Variables ***
+
+# Timeout value in minutes. Default 3 minutes.
+${IPMI_POWEROFF_WAIT_TIMEOUT}    3
 
 *** Test Cases ***
 
@@ -57,7 +61,7 @@
 
     Redfish Power On  stack_mode=skip
     Run IPMI Standard Command  chassis power soft
-    Wait Until Keyword Succeeds  3 min  10 sec  Is Host Off Via IPMI
+    Wait Until Keyword Succeeds  ${IPMI_POWEROFF_WAIT_TIMEOUT} min  10 sec  Is Host Off Via IPMI
 
 
 Verify Chassis Power Cycle And Check Chassis Status Via IPMI