Add periodic task to rebuild conductor local state

This adds a periodic task which can rebuild the conductor's local state
(PXE config files, etc) when conductors join or leave the cluster.

For any node which is newly mapped to the conductor, this will
trigger calling prepare() and take_over() on that node's deploy
interface.

This uses the periodic_max_worker setting like other periodic jobs,
starting the take over process in separate threads. Thus, in a large
cluster, it may take some time for all nodes to settle down.
It also adds a new CONF option to control the timing of this job.

There is a lot of room for improvement and optimization in this, however
getting a fix in place is critical to the Juno release.

NOTE: This does not re-establish any console sessions.

Co-Authored-By: Lucas Alvares Gomes <lucasagomes@gmail.com>
Change-Id: I0dbe9a5a98ec5fd0c69f32d7590d8141da5a23c2
Closes-bug: #1279331