Make sure all geth processes are killed when stopping a local testnet (#5383)

* Fix geth processes not being killed when stopping a local testnet

* Merge branch 'unstable' of https://github.com/sigp/lighthouse into fix_stop_testnet

Author: danielrachi1

scripts/local_testnet/geth.sh

@@ -50,5 +50,4 @@ exec $GETH_BINARY \
     --bootnodes $EL_BOOTNODE_ENODE \
     --port $network_port \
     --http.port $http_port \
-    --authrpc.port $auth_port \
-    2>&1 | tee $data_dir/geth.log
+    --authrpc.port $auth_port