To be able to easily plug-in future types of ways to get
which topics (and tasks) workers exist on (and can perform)
and to identify and keep this information up-to date refactor
the functionality that currently does this using periodic messages
into a finder type and a periodic function that exists on
it (that will be periodically activated by an updated and
improved periodic worker).
Part of blueprint wbe-worker-info
Change-Id: Ib3ae29758af3d244b4ac4624ac380caf88b159fd