shared/tester: Fix teardown multiple times
shared/tester: Fix teardown multiple times

tester_test* can be called multiple times which cause teardown callback
to be called multiple times as well leading to to crashes or strange
behavior.

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