SSDM-2718: system tests for the new type of service

openbis/sourceTest/core-plugins/core-plugins.properties

...i-services/1/as/services/simple-service/plugin.properties

...est-v3api-services/1/as/services/simple-service/script.py

...thz/sis/openbis/systemtest/api/v3/ExecuteServiceTest.java

...ethz/sis/openbis/systemtest/api/v3/SearchServiceTest.java

...a/ch/systemsx/cisd/openbis/systemtest/SystemTestCase.java