virExec will write out the pid of the daemonized process only. Use this
in the QEMU driver, rather than QEMU's pidfile, so we can catch errors we
might miss if the emulator bails early.

Seems like a simple typo - it has been "format=" since the flag
was introduced, but we added it as "fmt=".
Signed-off-by: NMark McLoughlin <markmc@redhat.com>

* tests/qemuxml2argvtest.c (testCompareXMLToArgvFiles): Adjust the
code that creates "actual" output, so that it too produces a
newline-terminated buffer.
* tests/qemuxml2argvdata/*.args: Append a newline to each, via:
for i in $(find|grep '\.args$'); do echo >> $i;done

handling code.  In particular, if you had a section of XML like:

    <disk type='file' device='cdrom'>
      <target dev='hdc' bus='ide'/>
      <readonly/>
    </disk>

This used to work with older libvirt, but now fails.  This is because we are
actually passing the literal string (null) to the qemu command-line, which qemu
barfs on.  This patch fixes it up by making it blank, which allows qemu to
continue on it's merry way.
Signed-off-by: NChris Lalancette <clalance@redhat.com>