reboot-ping-pong: Cope with new petitboot PS1

It appears to have removed the path element, so make it optional in the
pexpect regex.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: Ice5a253895690edda2d1bef80b010fbcb693f512
diff --git a/amboar/obmc-scripts/reboot-ping-pong/rpp b/amboar/obmc-scripts/reboot-ping-pong/rpp
index c4940a9..251e250 100755
--- a/amboar/obmc-scripts/reboot-ping-pong/rpp
+++ b/amboar/obmc-scripts/reboot-ping-pong/rpp
@@ -104,7 +104,7 @@
 
 class Host(object):
     def __init__(self, entity, bmc):
-        self.shell = "/ #".encode()
+        self.shell = "/? *#".encode()
         self.petitboot = "Petitboot".encode()
         self.session = None
         self.entity = entity