devtool: add download_ci_artifacts command

Every now and then, I managed to end up with an empty CI artifacts
folder, for whatever reason (mostly me being silly). The solution is
generally to remove whatever messed up stuff I ended up with in
build/img, and run some arbitrary devtool command that I know will
redownload everything. Similar workflows must happen whenever we do an
in-place update of our CI artifacts.

Abstract this away into a command that deletes the build/img folder, and
then redownloads it.

Signed-off-by: Patrick Roy <[email protected]>

tools/devtool

@@ -418,6 +418,10 @@ cmd_help() {
     echo "        Builds the rootfs and guest kernel artifacts we use for our CI."
     echo "        Run './tools/devtool build_ci_artifacts help' for more details about the available commands."
     echo ""
+    echo "    download_ci_artifacts [--force]"
+    echo "        Downloads the CI artifacts used for testing from our S3 bucket. If --force is passed, purges any existing"
+    echo "        artifacts first. Useful for refreshing local artifacts after an update, or if something got messed up."
+    echo ""
 
     cat <<EOF
     test_debug [-- [<pytest args>]]
@@ -555,6 +559,14 @@ cmd_distclean() {
     fi
 }
 
+cmd_download_ci_artifacts() {
+    if [ "$1" = "--force" ]; then
+        rm -rf $FC_BUILD_DIR/img
+    fi
+
+    ensure_ci_artifacts
+}
+
 ensure_ci_artifacts() {
     if ! command -v aws >/dev/null; then
       die "AWS CLI not installed, which is required for downloading artifacts for integration tests."