su01: fix the uncompleted string match

We find that sometimes "spawn /bin/su -l $USER1 -c whoami"
may return two lines:
"Attempting to create directory /home/su_usr2/perl5"
"su_usr2"
So the uncompleted "su_usr2" string match the first line,
but we expect to match the second line here.
So, fix it to match "su_usr2\r" instead.

Reported-by: DAN LI <li.dan@cn.fujitsu.com>
Signed-off-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>