fixup: bsc: Add testscase & infra to validate Osmux support BTS<->BSC

The per-BTS VTY command 'osmux (on|off|only)' was added to osmo-bsc.git
recently, and is not available in -latest yet.  Use it conditionally.

Change-Id: Id501d3f4b5eb18b096d8baffcb5f38e583f7a3d8
Fixes: I6e82eb9d995de988b812001e1c4cf6923509de66
1 file changed