discussion_sync: commit after creating each ticket
I noticed that when I abort sync-discussions with Ctrl+C, some of the tickets
get created, but are not saved in the DB, and therefore another sync-discussions
will create tickets for those bugs again (duplicating, triplicating them, etc).
While I did that with Ctrl+C, a network error could have a similar effect.
When creating discussion tickets, let's commit it to DB after each new ticket is
created. It doesn't slow us down in any meaningful way and it's more error-prone
against errors and therefore multiplicated tickets.
Fixes https://pagure.io/fedora-qa/blockerbugs/pull-request/158