This adds management/persistence.zeek to establish common configuration for log
rotation and persistent variable state. Log-writing Zeek processes initially
write locally in their working directory, and rotate into subdirectory
"log-queue" of the spool. Since agent and controller have no logger,
persistence.zeek puts in place compatible configurations for them.
Storage folders for Broker-backed tables and clusterized stores default to
subdirectories of the new Zeek-level state folder.
When setting the ZEEK_MANAGEMENT_TESTING environment variable, persistent state
is kept in the local directory, and log rotation remains disabled.
This also tweaks @loads a bit in favor of simply loading frameworks/management,
which is easier to keep track of.
