test: support local-first testing

Cherry-picked from coop-cloud/abra#389

Thanks @p4u1.

tests/integration/helpers/server.bash

@@ -1,7 +1,11 @@
 #!/usr/bin/env bash
 
 _add_server() {
-  run $ABRA server add "$TEST_SERVER"
+  if [[ "$TEST_SERVER" == "default" ]]; then
+      run $ABRA server add -l
+  else
+      run $ABRA server add "$TEST_SERVER"
+  fi
   assert_success
   assert_exists "$ABRA_DIR/servers/$TEST_SERVER"
 }