This patch cleans up building the "-boot" parameter and while on that
fixes one inconsistency by modifying these things:
- I completed the unfinished virDomainBootMenu enum by specifying
LAST, declaring it and also declaring the TypeFromString and
TypeToString parameters.
- Previously mentioned TypeFromString and TypeToString are used when
parsing the XML.
- Last, but not least, visible change is that the "-boot" parameter
is built and parsed properly:
- The "order=" prefix is used only when additional parameters are
used (menu, etc.).
- It's rewritten in a way that other parameters can be added
easily in the future (used in following patch).
- The "order=" parameter is properly parsed regardless to where it
is placed in the string (e.g. "menu=on,order=nc").
- The "menu=" parameter (and others in the future) are created
when they should be (i.e. even when bootindex is supported and
used, but not when bootloader is selected).
Prefer bootindex=N option for -device over the old way -boot ORDER
possibly accompanied with boot=on option for -drive. This gives us full
control over which device will actually be used for booting guest OS.
Moreover, if qemu doesn't support boot=on, this is the only way to boot
of certain disks in some configurations (such as virtio disks when used
together IDE disks) without transforming domain XML to use per device
boot elements.
