There are no options to parse here other than the name of the device,
and all three possible device names have the same prefix
("virtio-balloon" with "-ccw", "-pci", or "-device" appended), so the
code is fairly simple. It has been implemented such that it will be
easier to add handling for other -device entries that aren't otherwise
recognized - just add another "else if (STRPREFIX(opts, ....)" clause.
qemuParseCommandLineString() previously would always add a <memballoon
model='virtio'/> to every result (the comments erroneously say that it
is adding a <memballoon model='none'/>) This has been changed to add
model='none', and 84 test case xml's updated accordingly (so that
qemuxml2argvtest won't fail).
Now that the memballoon device is properly parsed, we can safely add a
test for properly ignoring -nodefconfig and -nodefaults. Rather than
adding an entire new test case for this (and memballoon), we just
randomly pick the clock-utc test and modify it slightly to fulfill the
purpose.
<controller type='pci' index='0' model='pci-root'/>
is auto-added to pc* machine types.
Without this controller PCI bus 0 is not available and
no PCI addresses are assigned by default.
Since older libvirt supported PCI bus 0 even without
this controller, it is removed from the XML when migrating.
