Add synchronization of configuration for HA hubs.

Synchronize notification_scripts directory to copy notifications scripts
form active to passive hubs.
DON'T use u_rcp for copying files from one hub to another.
Allow access to needed configuration files for all hubs in HA installation.
When adding things that use `admit => { @(def.policy_servers) }`, please precede this with
```
      admit_hostnames => { @(def.acl_hostnames) },
      admit_ips => { @(def.acl_ips) },
```
so that the modern versions are treated as first-class citizens (while still retaining the old until it's officially retired).