Update VM creation script to install GCP Python library

...kerfile/stress_test/grpc_interop_stress_csharp/Dockerfile

...s_test/grpc_interop_stress_csharp/build_interop_stress.sh

...dockerfile/stress_test/grpc_interop_stress_cxx/Dockerfile

...ress_test/grpc_interop_stress_cxx/build_interop_stress.sh

.../dockerfile/stress_test/grpc_interop_stress_go/Dockerfile

...tress_test/grpc_interop_stress_go/build_interop_stress.sh

...ockerfile/stress_test/grpc_interop_stress_java/Dockerfile

...ess_test/grpc_interop_stress_java/build_interop_stress.sh

...ockerfile/stress_test/grpc_interop_stress_node/Dockerfile

...ess_test/grpc_interop_stress_node/build_interop_stress.sh

...dockerfile/stress_test/grpc_interop_stress_php/Dockerfile

...ress_test/grpc_interop_stress_php/build_interop_stress.sh

...kerfile/stress_test/grpc_interop_stress_python/Dockerfile

...s_test/grpc_interop_stress_python/build_interop_stress.sh

...ockerfile/stress_test/grpc_interop_stress_ruby/Dockerfile

...ess_test/grpc_interop_stress_ruby/build_interop_stress.sh

tools/gce/linux_worker_init.sh