vty_transcript_test.vty: add choice auto-complete tests

This patch is a result of discussion we had in [1]. The key idea
is that libosmovty should properly auto-complete the commands
containing choice, such as the following one:

  multi0 (one|two|three)

[1] If9b0c0d031477ca87786aab5c269d00748e896c8

Right now, sending the following command:

  (osmo-foo-bar)# multi0 th

would basically match the following vector:

  multi0 three

however the resulting argv would be:

  ["multi0", "th"]

Moreover, sending the following command:

  (osmo-foo-bar)# multi0 t

would basically match the following vectors:

  multi0 two
  multi0 three

because both start from 't', so the resulting argv would be:

  ["multi0", "t"]

which is ambiguous!

The expected output is:

  (osmo-foo-bar)# multi0 th
  ok argc=1 three

  (osmo-foo-bar)# multi0 t
  % Ambiguous command.

This is going to be fixed in the follow up patches.

Change-Id: I83c3aef813173952641035862c534ef16384780e
diff --git a/tests/vty/vty_transcript_test.vty b/tests/vty/vty_transcript_test.vty
index 57920a8..27dacdc 100644
--- a/tests/vty/vty_transcript_test.vty
+++ b/tests/vty/vty_transcript_test.vty
@@ -66,3 +66,12 @@
 
 vty_transcript_test> multi2
 ok argc=0
+
+vty_transcript_test> multi0 thr
+ok argc=1 thr
+
+vty_transcript_test> multi1 on
+ok argc=1 on
+
+vty_transcript_test> multi2 t
+ok argc=1 t