Commit 119cd06e started setting the primary bool for the first
user-specified video even if user omitted the 'primary' attribute.

However this was done before the addition of the implicit device.
This broke startup of transient qemu domains with no <video>:
https://bugzilla.redhat.com/show_bug.cgi?id=1325757

Move this default to virDomainDefPostParseInternal,
after the addition of the implicit video device, to catch the implicit
video as well.

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

The memory XML blanking is only there to avoid the unit= churn that
was added by default a long time ago.

Drop the blanking, switch over to using the standard comparison
helpers, and regenerate the output with VIR_TEST_REGENERATE_OUTPUT.

If a qemuargv has iscsi or ceph secrets on the command line, we will
convert that to XML like:

  <auth username='myname'>
    <secret type='iscsi'/>
  </auth>

This is not valid XML, as either a UUID or usage must be specified in
the secret block. It's not clear though how the argv2xml code can do
anything correct here, since XML like this requires a libvirt secret
object to have already been defined.

The current test suite handles this by blanking out any <secret> block
in the XML. This avoids domainschematest failures.

Instead of blanking, let's hardcode a usage= name. This lets us test
the other bits of generated <secret> XML, and is a step towards wiring
up VIR_TEST_REGENERATE_OUTPUT

Overwrite any randomly generated UUID to use a hardcoded value, so
we don't need to blank it when comparing XML.

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.