Change the name from Immediate to On-Demand for CPU Log

The name "Immediate" was confusing, so changing the name to
"OnDemand" to make it's purpose more clear.

Tested:
Used Postman to send a POST to "/redfish/v1/Systems/system/
LogServices/CpuLog/Actions/Oem/CpuLog.OnDemand" and verified
that the expected On-Demand data was returned.

Change-Id: If9b6b30e1c424227601fb6b7381470f571afca9e
Signed-off-by: Jason M. Bills <jason.m.bills@linux.intel.com>