Changes

tests/vty: Add vty-transcript-test for osmo-stp

So far we were only testing vty transcript for libosmo-sccp in ASP mode
(osmo_ss7_vty_init_asp()). Let's also test in SG mode
(osmo_ss7_vty_init_sg()), the one used in osmo-stp.

Last command in SG-only node "route-table system" shows a current bug in
command "update route", returning "% Unknown command.".

Related: OS#6586
Change-Id: If2f069b9d724038c326f5c35848faa1e9c216fd5