A feature new in Python 2.7 crept into commit 77e703b8: re.subn()'s
fifth argument.  Avoid that, use re.compile().
Reported-by: NLaurent Desnogues <laurent.desnogues@gmail.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Tested-by: NLaurent Desnogues <laurent.desnogues@gmail.com>
Message-id: 1441640755-23902-1-git-send-email-armbru@redhat.com
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>