qemuxml2argv: Add test to verify correct usage of disk type="volume"

Tweak the existing file to test command line generator too.

tests/qemuxml2argvdata/qemuxml2argv-disk-source-pool.args

+LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test QEMU_AUDIO_DRV=none \
+/usr/bin/qemu -S -M pc -m 214 -smp 1 -nographic -nodefconfig -nodefaults \
+-monitor unix:/tmp/test-monitor,server,nowait -no-acpi -boot c -usb -drive \
+file=/some/block/device/cdrom,if=none,media=cdrom,id=drive-ide0-0-1 -device \
+ide-drive,bus=ide.0,unit=1,drive=drive-ide0-0-1,id=ide0-0-1 -drive \
+file=/tmp/idedisk.img,if=none,id=drive-ide0-0-2 -device \
+ide-drive,bus=ide.0,unit=2,drive=drive-ide0-0-2,id=ide0-0-2 -device \
+virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x4

tests/qemuxml2argvdata/qemuxml2argv-disk-source-pool.xml

@@ -15,7 +15,7 @@
   <devices>
     <emulator>/usr/bin/qemu</emulator>
     <disk type='volume' device='cdrom'>
-      <source pool='blk-pool0' volume='blk-pool0-vol0' startupPolicy='optional'>
+      <source pool='pool-disk' volume='block+cdrom'>
         <seclabel model='selinux' relabel='yes'>
           <label>system_u:system_r:public_content_t:s0</label>
         </seclabel>

tests/qemuxml2argvtest.c

@@ -791,6 +791,8 @@ mymain(void)
     DO_TEST("disk-aio",
             QEMU_CAPS_DRIVE, QEMU_CAPS_DRIVE_AIO,
             QEMU_CAPS_DRIVE_CACHE_V2, QEMU_CAPS_DRIVE_FORMAT);
+    DO_TEST("disk-source-pool",
+            QEMU_CAPS_DRIVE, QEMU_CAPS_DEVICE, QEMU_CAPS_NODEFCONFIG);
     DO_TEST("disk-ioeventfd",
             QEMU_CAPS_DRIVE, QEMU_CAPS_VIRTIO_IOEVENTFD,
             QEMU_CAPS_VIRTIO_TX_ALG, QEMU_CAPS_DEVICE,