qemu: Remove extra messages from virtio-scsi hotplug

I tried to attach a SCSI LUN to two different guests, and forgot
to specify "shareable" in the hostdev XML.  Attaching the device
to the second guest failed, but the message was not helpful in
telling me what I was doing wrong:

  $ cat scsi_scratch_disk.xml
    <hostdev mode='subsystem' type='scsi'>
      <source>
        <adapter name='scsi_host3'/>
        <address bus='0' target='15' unit='1074151456'/>
      </source>
    </hostdev>

  $ virsh attach-device dasd_sles_d99c scsi_scratch_disk.xml
  Device attached successfully

  $ virsh attach-device dasd_fedora_0e1e scsi_scratch_disk.xml
  error: Failed to attach device from scsi_scratch_disk.xml
  error: internal error: Unable to prepare scsi hostdev: scsi_host3:0:15:1074151456

I eventually discovered my error, but thought it was weird that
Libvirt doesn't provide something more helpful in this case.
Looking over the code we had just gone through, I commented out
the "internal error" message, and got something more useful:

  $ virsh attach-device dasd_fedora_0e1e scsi_scratch_disk.xml
  error: Failed to attach device from scsi_scratch_disk.xml
  error: Requested operation is not valid: SCSI device 3:0:15:1074151456 is already in use by other domain(s) as 'non-shareable'

Looking over the error paths here, we seem to issue better
messages deeper in the callchain so these "internal error"
messages overwrite any of them.  Remove them, so that the
more detailed errors are seen.
Signed-off-by: NEric Farman <farman@linux.vnet.ibm.com>
(cherry picked from commit 33c1fc43)

src/qemu/qemu_hotplug.c

@@ -2467,23 +2467,8 @@ qemuDomainAttachHostSCSIDevice(virConnectPtr conn,
             return -1;
     }
 
-    if (qemuHostdevPrepareSCSIDevices(driver, vm->def->name,
-                                      &hostdev, 1) < 0) {
-        virDomainHostdevSubsysSCSIPtr scsisrc = &hostdev->source.subsys.u.scsi;
-        if (scsisrc->protocol == VIR_DOMAIN_HOSTDEV_SCSI_PROTOCOL_TYPE_ISCSI) {
-            virDomainHostdevSubsysSCSIiSCSIPtr iscsisrc = &scsisrc->u.iscsi;
-            virReportError(VIR_ERR_INTERNAL_ERROR,
-                           _("Unable to prepare scsi hostdev for iSCSI: %s"),
-                           iscsisrc->path);
-        } else {
-            virDomainHostdevSubsysSCSIHostPtr scsihostsrc = &scsisrc->u.host;
-            virReportError(VIR_ERR_INTERNAL_ERROR,
-                           _("Unable to prepare scsi hostdev: %s:%u:%u:%llu"),
-                           scsihostsrc->adapter, scsihostsrc->bus,
-                           scsihostsrc->target, scsihostsrc->unit);
-        }
+    if (qemuHostdevPrepareSCSIDevices(driver, vm->def->name, &hostdev, 1) < 0)
         return -1;
-    }
 
     if (qemuDomainNamespaceSetupHostdev(driver, vm, hostdev) < 0)
         goto cleanup;