tools: Fix clearing event filters in notifier

Fixes clearing event filters in notifier. If you had this configuration
FILTERS=exclude:* (default) and after that you add notification to some
user in webadmin, no email was sent until notifier is restarted due to
inproper clearing of event filters.

Change-Id: If665a84b1c18af1318b74bd88d134164f0f3476c
Bug-Url: https://bugzilla.redhat.com/1071536
Signed-off-by: Martin Perina <mperina@redhat.com>