Add a common api for hardware raid configuration

It's common requirement that the users or system admins need to configure hardware raid for the baremetal servers, but different venders use different configuration tool to do it, this blueprint is to provide a common api in Ironic to configure hardware raid.

Simply providing a common api will not enable utility ramdisk (e.g. python-ironic-agent) to actually go as far as setting up a hardware raid, due to differing setting tools published by each vendor; however, we will consider this function on the premise of the user adding their own vendor's tool to element of diskimage-builder.