SAR-276 Added multidevice tests

src/ska_tango_base/base/base_device.py

src/ska_tango_base/base/reference_component_manager.py

src/ska_tango_base/utils.py

tests/conftest.py

tests/long_running_tasks/conftest.py

tests/long_running_tasks/reference_base_device.py

tests/long_running_tasks/test_multi_device.py

tests/long_running_tasks/test_reference_base_device.py