Bug 1937982: Making sure report downloads have unique names

Fixed a problem where two reports had the same name and also made a
change where the datestamp for the CSV file is added to the name in
case browsers are caching them and so fetching cached one instead of
newly generated one.

Change-Id: Id0f4ae007dbc96aab76842a7ffae7acbf391d6af
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>
(cherry picked from commit 9ae952e3)