commit 8d04f95d96f869543a99b18fd3326ea84e9f5366
author Neels Hofmeyr <neels@hofmeyr.de> Fri Feb 01 00:25:55 2019 +0100
committer Neels Hofmeyr <nhofmeyr@sysmocom.de> Mon Feb 04 16:43:57 2019 +0000
tree 4cba29140ead2a5124dbec7aea826985a65fa6d6
parent 9ea9dd0d5fdad50d9b2ea2bdddd9d919efab31ca

vty telnet: consistently never change nodes upon CTRL-C

Remove any special node exiting from the VTY CTRL-C handling.

From a curious VTY transcript test glitch, I noticed weird behavior by the VTY
telnet shell: usually, when the user hits CTRL-C, that means to cancel the
current command line and present a fresh, clean prompt. However, only on the
CONFIG_NODE and CFG_LOG_NODE, a CTRL-C also exits the current node and moves up
by one level. This behavior is unexplainable and makes zero sense.

No other nodes exit on CTRL-C:
- on the ENABLE node, a CTRL-C stays on the ENABLE_NODE and doesn't exit to the
  VIEW_NODE.
- any sub-nodes of the CONFIG_NODE stay unchanged, e.g. 'network' or 'bts' /
  'trx', etc.

There is no apparent special meaning of CTRL-C on CONFIG_NODE nor CFG_LOG_NODE
to justify this odd choice.

Particularly, the vty transcript tests using osmo_verify_transcript_vty.py rely
on sending CTRL-C to clear the command prompt, so that we can properly test
sending '?' to the VTY during transcripts. In a live session, a '?' prints
available options and then updates the prompt with identical command arguments.
In a transcript test, that doesn't make sense, because each time the transcript
writes out a new command to run. Consider e.g. a transcript test like:

	tdef_vty_test(config)# timer ?
	  tea       Tea time
	  test      Test timers
	  software  Typical software development cycle

	tdef_vty_test(config)# timer tea ?
	  [TNNNN]  T-number, optionally preceded by 't' or 'T'.

To be able to issue a fresh command after '?', osmo_verify_transcript_vty.py
explicitly sends a CTRL-C to clear the command buffer. Hence there we rely on
predictable behavior of CTRL-C.

More particularly, the upcoming osmo_tdef_vty transcript tests are apparently
the first that want to test '?' behavior on the CONFIG_NODE's root level and
fall on their face, because of the implicit exit that happens only there.

Change-Id: I4f339ba61f1c273fa7da85caf77ba116ae2697b1