Fix mock import in tests.
Fix mock import in tests.

For some reason, one test imports Mock class from mock.mock
rather than from mock.
This change fixes this error.

Signed-off-by: Oleg Girko <665b39a1e96a9a15fc99f73183af3f04bf8111eb@infoserver.lv>

TribeMedia/synapse,TribeMedia/synapse,iot-factory/synapse,TribeMedia/synapse,matrix-org/synapse,iot-factory/synapse,matrix-org/synapse,matrix-org/synapse,TribeMedia/synapse,matrix-org/synapse,TribeMedia/synapse,iot-factory/synapse,matrix-org/synapse,iot-factory/synapse,matrix-org/synapse,iot-factory/synapse