fix PR #1567

PR  #1567 fixed an issue where ssh server would not recognize custom
ssh server ports.  However, it broke another case by forcing
local username if it is unspecified.

ssh config should be trusted with the default username.

IPython/external/ssh/tunnel.py

@@ -208,9 +208,13 b" def openssh_tunnel(lport, rport, server, remoteip='127.0.0.1', keyfile=None, pas"
     ssh="ssh "
     if keyfile:
         ssh += "-i " + keyfile
-    username, server, port = _split_server(server)
-    cmd = "%s -p %s -f -L 127.0.0.1:%i:%s:%i %s@%s sleep %i" % (
-        ssh, port, lport, remoteip, rport, username, server, timeout)
+    
+    if ':' in server:
+        server, port = server.split(':')
+        ssh += " -p %s" % port
+        
+    cmd = "%s -f -L 127.0.0.1:%i:%s:%i %s sleep %i" % (
+        ssh, lport, remoteip, rport, server, timeout)
     tunnel = pexpect.spawn(cmd)
     failed = False
     while True: