runqemu: Use virtio to mount cdrom drives

The IDE driver in the kernel is fragile and in 4.12 is causing backtraces.
To unblock 4.12 kernel merging use the virtio CD driver instead to mount
iso images which should be faster and more stable.

(From OE-Core rev: f59e729f98ef9b506b0cfdc415567e03ec87f2a9)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/runqemu

@@ -1005,7 +1005,7 @@ class BaseConfig(object):
             vm_drive = ''
             if self.fstype in self.vmtypes:
                 if self.fstype == 'iso':
-                    vm_drive = '-cdrom %s' % self.rootfs
+                    vm_drive = '-drive file=%s,if=virtio,media=cdrom' % self.rootfs
                 elif self.get('QB_DRIVE_TYPE'):
                     drive_type = self.get('QB_DRIVE_TYPE')
                     if drive_type.startswith("/dev/sd"):