Simplify checksum commands for consistency

.circleci/config.yml

@@ -177,14 +177,14 @@ references:
     run:
       name: Pre Checkout
       command: |
-        mkdir -p $ROS_WS
-        ln -s /opt/ros/$ROS_DISTRO $ROS_WS/install
+        mkdir -p $ROS_WS && cd $ROS_WS
+        ln -s /opt/ros/$ROS_DISTRO install
         echo $CACHE_NONCE | \
-          (echo cache_nonce && cat) >> $ROS_WS/checksum.txt
-        sha256sum $ROS_WS/checksum.txt >> $ROS_WS/checksum.txt
+          (echo cache_nonce && cat) >> checksum.txt
+        sha256sum $PWD/checksum.txt >> checksum.txt
         TZ=utc stat -c '%y' /ros_entrypoint.sh | \
-          (echo ros_entrypoint && cat) >> $ROS_WS/checksum.txt
-        sha256sum $ROS_WS/checksum.txt >> $ROS_WS/checksum.txt
+          (echo ros_entrypoint && cat) >> checksum.txt
+        sha256sum $PWD/checksum.txt >> checksum.txt
         rm -rf $OVERLAY_WS/*
   on_checkout: &on_checkout
     checkout: