PostParse handles it for us now.
This causes some test suite churn; qemu's custom PostParse could is
now invoked before the generic AddImplicitControllers, so PCI
controllers end up sequentially in the XML before the generically
added IDE controllers. So it's just some XML reordering
Most of the qemuargv2xml tests are parsing old style qemu command
lines (with -disk, -serial, etc), and it gets its input from
qemuxml2argv output.
But since we've raise the minimum supported qemu version to 0.12.0,
which supports -device, once that changes propagates through libvirt
the vast majority of qemuxml2argv output is _not_ going to be using
old style qemu options.
In preparation for this, switch qemuargv2xml to use its own copies
of input and output, so it's not tied to qemuxml2argv results.
This is just a straight copy of the current tests.
