Ignore Telnet options. Addresses issue Juniper#44.

If no option negotiation callback function is set, telnetlib
will pass Telnet options back to netconify in the data stream.
This is especially problematic for the AUTHENTICATION (0x25) option.
0x25 is an ASCII % character and confuses the login state machine into
thinking that it is at the shell prompt.
This function simply receives and ignores Telnet options. This prevents
the options from appearing in the data stream and confusing the
login state machine.

lib/netconify/tty_telnet.py

@@ -7,6 +7,20 @@
 # Terminal connection over TELNET CONSOLE
 # -------------------------------------------------------------------------
 
+def _ignore_options(socket, command, option):
+    """
+    Used as a Telnet.set_option_negotiation_callback() function.
+
+    If no option negotiation callback function is set, telnetlib
+    will pass Telnet options back to netconify in the data stream.
+    This is especially problematic for the AUTHENTICATION (0x25) option.
+    0x25 is an ASCII % character and confuses the login state machine into
+    thinking that it is at the shell prompt.
+    This function simply receives and ignores Telnet options. This prevents
+    the options from appearing in the data stream and confusing the
+    login state machine.
+    """
+    pass
 
 class Telnet(Terminal):
     RETRY_OPEN = 3                # number of attempts to open TTY
@@ -41,6 +55,7 @@ def __init__(self, host, port, **kvargs):
 
     def _tty_open(self):
         retry = self.RETRY_OPEN
+        self._tn.set_option_negotiation_callback(_ignore_options)
         while retry > 0:
             try:
                 self._tn.open(self.host, self.port, self.timeout)