enable cloud_to_cloud tests with servers in a separate container

src/csharp/Grpc.IntegrationTesting/InteropClient.cs

tools/jenkins/build_docker_and_run_interop_tests.sh

tools/jenkins/docker_prepare_interop_tests.sh

tools/jenkins/docker_run_interop_servers.sh

tools/jenkins/docker_run_interop_tests.sh

tools/jenkins/docker_run_tests.sh

tools/jenkins/run_distribution.sh

tools/jenkins/run_jenkins.sh

tools/run_tests/run_interop_tests.py

tools/run_tests/run_tests.py