scouting: Make background_task interval configurable

This patch modifies the API so that the background task gets invoked
at a user-defined interval. There are no functional changes since we
schedule everything at 10 minute intervals. That matches the previous
behaviour.

Signed-off-by: Philipp Schrader <philipp.schrader@gmail.com>
Change-Id: I512ddcd01408f9d1af706ca390c84368f6816638
diff --git a/scouting/webserver/rankings/rankings_test.go b/scouting/webserver/rankings/rankings_test.go
index 03a4ac6..4ab3c34 100644
--- a/scouting/webserver/rankings/rankings_test.go
+++ b/scouting/webserver/rankings/rankings_test.go
@@ -38,7 +38,7 @@
 
 func TestGetRankings(t *testing.T) {
 	database := MockDatabase{}
-	scraper := background_task.BackgroundTask{}
+	scraper := background_task.New(time.Minute)
 	tbaServer := server.NewScoutingServer()
 	tbaServer.Handle("/", ServeRankings(t, http.FileServer(http.Dir("../../"))))
 	tbaServer.Start(8000)