close the http filehandle in resp.Body

its noted in the docs and basically everywhere that if you don't
explicitly close the filehandle, it stays open forever.

I should probably look into setting timeouts for the /ping page.
set read/write timeouts for http server

don't let the filehandles pile up
Merge pull request #4 from coffeepac/close-http-filehandles

Close http filehandles