Add avtest support for arbitrary commands
Add avtest support for arbitrary commands

This is useful e.g. invalid signal identifier AVDTP tests.

pkarasev3/bluez,pstglia/external-bluetooth-bluez,pstglia/external-bluetooth-bluez,silent-snowman/bluez,ComputeCycles/bluez,mapfau/bluez,ComputeCycles/bluez,pstglia/external-bluetooth-bluez,mapfau/bluez,mapfau/bluez,silent-snowman/bluez,pkarasev3/bluez,pkarasev3/bluez,silent-snowman/bluez,pkarasev3/bluez,ComputeCycles/bluez,pstglia/external-bluetooth-bluez,mapfau/bluez,ComputeCycles/bluez,silent-snowman/bluez