When there is a hashsum mismatch diskimage-builder forces downloads
with the -f switch of cache-url. This is currently broken because bash
escapes the quotes in curl_opts. This tricks curl trying to download
'no-cache' instead of the url. This can be fixed by using an array for
curl_opts which does the correct thing here.
Change-Id: Id9f1579dda9a3e0a2b08dd5faaeef0e2e580d419
bad433fa92