added constants to several tests

...ationcontrol/tangostationcontrol/test/beam/test_delays.py

...control/tangostationcontrol/test/common/test_baselines.py

...gostationcontrol/test/devices/test_antennafield_device.py

...l/tangostationcontrol/test/devices/test_beamlet_device.py

...ngostationcontrol/test/devices/test_digitalbeam_device.py

...trol/tangostationcontrol/test/devices/test_recv_device.py