This would fix long standing failures running tests on
my development machine, which set `Gitlab.config.gitlab.host`
to another host because it's not my local computer. Now I
finally cannot withstand it and decided to fix them once and
for all.
Related to #2235.
This is done by:
1. Delaying the notification sending after the SSH key is commited in DB
2. Gracefully exit the mailer method if the record cannot be found
