Add IPMI_POWEROFF_WAIT_TIMEOUT varaible for user input
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 <bef0a9ecac45fb57611777c8270153994e13fd2e@in.ibm.com>

openbmc/openbmc-test-automation,openbmc/openbmc-test-automation