conf: Fix the bug of disk->copy_on_read formating

The reason for it's not exposed for such long time is that the
enums for VirtioEventIdx and CopyOnReadType have same enum values
and Correspondingstrings. This fixes the bug and adds test.

src/conf/domain_conf.c

@@ -13708,7 +13708,7 @@ virDomainDiskDefFormat(virBufferPtr buf,
     const char *iomode = virDomainDiskIoTypeToString(def->iomode);
     const char *ioeventfd = virDomainIoEventFdTypeToString(def->ioeventfd);
     const char *event_idx = virDomainVirtioEventIdxTypeToString(def->event_idx);
-    const char *copy_on_read = virDomainVirtioEventIdxTypeToString(def->copy_on_read);
+    const char *copy_on_read = virDomainDiskCopyOnReadTypeToString(def->copy_on_read);
     const char *sgio = virDomainDiskSGIOTypeToString(def->sgio);
     const char *discard = virDomainDiskDiscardTypeToString(def->discard);
 

tests/qemuxml2argvdata/qemuxml2argv-disk-copy_on_read.xml

 <domain type='qemu'>
   <name>test</name>
+  <uuid>468404ad-d49c-40f2-9e14-02294f9c1be3</uuid>
   <memory unit='KiB'>1048576</memory>
+  <currentMemory unit='KiB'>1048576</currentMemory>
   <vcpu placement='static'>1</vcpu>
   <os>
     <type arch='x86_64' machine='pc-0.13'>hvm</type>
@@ -27,20 +29,23 @@
       <readonly/>
       <address type='drive' controller='0' bus='1' target='0' unit='0'/>
     </disk>
+    <controller type='usb' index='0'/>
+    <controller type='virtio-serial' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
+    </controller>
+    <controller type='ide' index='0'/>
+    <controller type='pci' index='0' model='pci-root'/>
     <interface type='user'>
       <mac address='52:54:00:e5:48:58'/>
       <model type='virtio'/>
       <driver name='vhost' txmode='iothread'/>
     </interface>
-    <controller type='usb' index='0'/>
-    <controller type='virtio-serial' index='0'>
-      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
-    </controller>
     <serial type='pty'>
       <target port='0'/>
     </serial>
     <console type='pty'>
       <target type='serial' port='0'/>
     </console>
+    <memballoon model='virtio'/>
   </devices>
 </domain>

tests/qemuxml2xmltest.c

@@ -293,6 +293,8 @@ mymain(void)
     DO_TEST("hostdev-scsi-virtio-scsi");
     DO_TEST("hostdev-scsi-readonly");
 
+    DO_TEST("disk-copy_on_read");
+
     virObjectUnref(driver.caps);
     virObjectUnref(driver.xmlopt);