get rid of using python2/python3 explicitly

CMakeLists.txt

CMakeModules/CodeCoverage.cmake

consumer/api/cpp/src/server_data_broker.cpp

consumer/api/cpp/unittests/test_server_broker.cpp

docs/sphinx/CMakeLists.txt

examples/consumer/getnext_broker_python/CMakeLists.txt

examples/consumer/getnext_broker_python/check_linux.sh

examples/pipeline/in_to_out_python/CMakeLists.txt

...utomatic/bug_fixes/consumer_python_memleak/CMakeLists.txt

...utomatic/bug_fixes/consumer_python_memleak/check_linux.sh

...s/error-sending-data-using-callback-method/CMakeLists.txt

...s/error-sending-data-using-callback-method/check_linux.sh

tests/automatic/common/cpp/src/testing.cpp

tests/automatic/consumer/consumer_api/consumer_api.cpp

tests/automatic/consumer/consumer_api_python/CMakeLists.txt

tests/automatic/consumer/consumer_api_python/check_linux.sh

...ic/full_chain/simple_chain_usermeta_python/CMakeLists.txt

...ic/full_chain/simple_chain_usermeta_python/check_linux.sh

tests/automatic/producer/python_api/CMakeLists.txt

tests/automatic/producer/python_api/check_linux.sh