vty: allow configuring db path from cfg file

So far, the cmdline argument was the only way to set a database file.
Add a similar config to VTY as 'msc' / 'sms-database'. The cmdline arg is stronger
than the 'database' cfg item. DB is not reloaded from VTY command.

Change-Id: I18d954c30fcceb0b36a620b927fd3a93dcc79f49
diff --git a/tests/test_nodes.vty b/tests/test_nodes.vty
index 520f07c..d389675 100644
--- a/tests/test_nodes.vty
+++ b/tests/test_nodes.vty
@@ -46,6 +46,7 @@
 OsmoMSC(config)# msc
 OsmoMSC(config-msc)# list
 ...
+  sms-database PATH
   assign-tmsi
   mncc internal
   mncc external MNCC_SOCKET_PATH