fix bug 1224381 - Poll import every 1 second
fix bug 1224381 - Poll import every 1 second

When running a long import, poll the server to see if the import is
complete every second, instead of immediately after getting the last
poll response.

mdn/browsercompat,jwhitlock/web-platform-compat,mdn/browsercompat,jwhitlock/web-platform-compat,mdn/browsercompat,jwhitlock/web-platform-compat