qemuProcessSetupDisksTransientSnapshot: Skip enabling transientOverlayCreated flag
QEMU_DOMAIN_DISK_PRIVATE(disk)->transientOverlayCreated flag
gets true unexpectedly on qemuProcessSetupDisksTransientSnapshot() when
the disk has <transient shareBacking='yes'> option.
The flag should be enabled on qemuDomainAttachDiskGeneric() after the
overlay setup is completed.
Skip enabling transientOverlayCreated for the disk here.
Fixes: 75871da0ecb8b552f9e304d0f83e216839bbf82d Signed-off-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com> Reviewed-by: Peter Krempa <pkrempa@redhat.com>