Improve bootstrapping

script/cardboard-exec

@@ -5,11 +5,15 @@ set -e
 
 cd $(dirname "$0")/..
 
-BIN=.bundle/binstubs
+BUNDLE=.bundle
+BIN=$BUNDLE/binstubs
 CARDBOARD=$BIN/cardboard
 SCRIPT=$(basename "$0")
 
-rm -rf .bundle/{binstubs,config}
+if [ -z "$SKIP_CARDBOARD_BOOTSTRAP" ]; then
+  rm -rf {$BIN,$BUNDLE/config}
+  bundle install --binstubs "$BIN" --path "$BUNDLE" --quiet
+  "$CARDBOARD" bootstrap
+fi
 
-bundle install --binstubs "$BIN" --path .bundle --quiet &&
-  "$CARDBOARD" bootstrap && exec "$CARDBOARD" "$SCRIPT" "$@"
+exec "$CARDBOARD" "$SCRIPT" "$@"