Use exec in geth start script to pass signals correctly (ethereum#868)

scripts/run_geth_in_docker.sh

@@ -1,11 +1,5 @@
-# allow exiting using CTRL + C
-exit_func() {
-        echo "Exiting..."
-        exit 1
-}
-trap exit_func SIGTERM SIGINT
-
+# Prevent error related to running geth without a tty
 # 150 is an arbitrary choice, which seems good enough
 stty cols 150
 sleep 1
-geth "$@"
+exec geth "$@"