Split overlay setup into multiple steps

by skipping slower to build leaf packages during preparation,
then store cache and repeat setup without skipping packages

.circleci/config.yml

@@ -123,6 +123,8 @@ _commands:
           type: string
         mixins:
           type: string
+        skip:
+          type: string
         build:
           default: true
           type: boolean
@@ -191,6 +193,7 @@ _commands:
                     . << parameters.underlay >>/install/setup.sh
                     colcon build \
                       --packages-select ${BUILD_PACKAGES} \
+                      --packages-skip < parameters.skip > \
                       --mixin << parameters.mixins >>
               - ccache_stats:
                   workspace: << parameters.workspace >>
@@ -364,6 +367,13 @@ _steps:
     install_dependencies:
       underlay: /opt/underlay_ws
       workspace: /opt/overlay_ws
+  prep_overlay_workspace: &prep_overlay_workspace
+    setup_workspace: &setup_workspace_overlay
+      key: overlay_ws
+      underlay: /opt/underlay_ws
+      workspace: /opt/overlay_ws
+      mixins: ${OVERLAY_MIXINS}
+      skip: nav2_system_tests
   setup_overlay_workspace: &setup_overlay_workspace
     setup_workspace: &setup_workspace_overlay
       key: overlay_ws
@@ -417,6 +427,7 @@ commands:
   build_source:
     description: "Build Source"
     steps:
+      - *prep_overlay_workspace
       - *setup_overlay_workspace
   restore_build:
     description: "Restore Build"