Preserve symlinks in --zip_undeclared_test_outputs

Update tools/test/test-setup.sh to preserve symlinks when performing the
zip of `$TEST_UNDECLARED_OUTPUTS_DIR`.

This fixes a serious bug where an absolute symlink generated in the test
could delete files anywhere on the filesystem.

For example, a `sh_test` containing a line like:

    ln -s "$HOME" "$TEST_UNDECLARED_OUTPUTS_DIR/home"

would have caused the users home directory to be deleted after copying
it in to the output.zip. With this change, the output.zip only contains
a (possibly dangling) symlink, but more importantly the deletions are
limited to the `$TEST_UNDECLARED_OUTPUTS_DIR`.

RELNOTES: `--zip_undeclared_test_outputs` now preserves symlinks when
zipping `$TEST_UNDECLARED_OUTPUTS_DIR`.

tools/test/test-setup.sh

@@ -427,7 +427,7 @@ if [[ -n "$TEST_UNDECLARED_OUTPUTS_ZIP" ]] && cd "$TEST_UNDECLARED_OUTPUTS_DIR";
     # Otherwise echo printed the top-level files and directories.
     # Pass files to zip with *, so paths with spaces aren't broken up.
     # Remove original files after zipping them.
-    zip -qrm "$TEST_UNDECLARED_OUTPUTS_ZIP" -- * 2>/dev/null || \
+    zip -qrmy "$TEST_UNDECLARED_OUTPUTS_ZIP" -- * 2>/dev/null || \
         echo >&2 "Could not create \"$TEST_UNDECLARED_OUTPUTS_ZIP\": zip not found or failed"
   fi
 fi