pty: unbreak libvirt

Commit 586502189edf9fd0f89a83de96717a2ea826fdb0 breaks libvirt pty
support because it tried to figure the pts name from stderr output.

Fix this by moving the label to the end of the line, this way the
libvirt parser does still recognise the message.  libvirt looks
for "char device redirected to ${ptsname}<whitespace>".

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>