add /etc/pmg/dkim to cluster-sync

add /etc/pmg/dkim to cluster-sync

The clustersync already uses rsync to sync most files (there are excludes
for '*.db', '*~', and the certificates of the node) from the master's
'/etc/pmg' directory to all nodes. Moving files from the syncdir to the node's
actual '/etc/pmg' happen only for explicitly listed files.

This patch adds a second list of explicit directories and adds
'/etc/pmg/templates' and '/etc/pmg/dkim' to that list.

The syncing of all files inside this directory list is done via
`rsync -aq --delete-after`. This is a semantic change to the loop used
for the templates directory, in which only regular files and symlinks were
copied (rsync copies everything recursively).

Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>