use run_tests_matrix.py for running internal_ci master tests

tools/internal_ci/linux/grpc_master.sh

@@ -47,12 +47,4 @@ git submodule update --init
 
 # download docker images from dockerhub
 export DOCKERHUB_ORGANIZATION=grpctesting
-tools/run_tests/run_tests.py -l c -t -x sponge_log.xml || FAILED="true"
-
-# kill port_server.py to prevent the build from hanging
-ps aux | grep port_server\\.py | awk '{print $2}' | xargs kill -9
-
-if [ "$FAILED" != "" ]
-then
-  exit 1
-fi
+tools/run_tests/run_tests_matrix.py -f basictests linux --internal_ci