Set chrome default download directory
Set chrome default download directory

By default chrome will download into a user's downloads directory. As these are automated tests we don't want to junk up the user's downloads folder, and as we don't actually care about the contents of the files (just the headers) it's fine to put them in a temp folder.

alphagov/digitalmarketplace-functional-tests,alphagov/digitalmarketplace-functional-tests,alphagov/digitalmarketplace-functional-tests