Retry to publish events indefinitely

When the plugin receives a ShutdownSignalException due to flaky LDAP
connections returning 403 Forbidden, it should not stop attempting to
publish events. Instead enter a 30s retry loop.

This will improve resiliency to network shakiness.

Solves: Jira GER-2002
Change-Id: Ia723c30099f17568a534f11b120088b14fe00a8d