su: ignore --preserve-environment, it's mutually exclusive to --login.

Listening on http://127.0.0.1:41739
R: src/unix/core.c:259: uv__finish_close: Assertion `!(handle->flags & UV_HANDLE_CLOSED)' failed.
-bash: line 1:  2528 Aborted                 R --no-save --slave -f \/opt\/shiny-server\/R\/SockJSAdapter\.R