Feature #2193: write osmo-gsm-tester test cases and extend tester API
osmo-gsm-tester: add test case: smpp: password
Test feature "password" from smpp vty. When this feature is on, the ESME requires a password.
Test it both negative + positive (on/off), (on: correct pwd, wrong pwd).
See smpp_vty.c in libmsc (openbsc) for more details.
Improve VTY doc if required.