tests/test_nodes.vty: check less libosmocore cmds

Use three dots to avoid checking for exact commands between help and
exit, which originate from libosmocore. This avoids test failues when
we slightly change the commands, like the change from "write file" to
"write file [PATH]" in [1] that is currently causing the vty tests to
fail.

[1] libosmocore I38edcf902a08b6bd0ebb9aa6fc1a7041421af525
Change-Id: I4a964b86195141e5a50705425206f3602f908999
1 file changed