propellor/TODO

* Need a way to run an action when a property changes, but only
  run it once for the whole. For example, may want to restart apache,
  but only once despite many config changes being made to satisfy
  properties. onChange is a poor substitute.
* Display of docker container properties is a bit wonky. It always
  says they are unchanged even when they changed and triggered a
  reprovision.
* Should properties be a tree rather than a list?
* Need a way for a dns server host to look at the properties of 
  the other hosts and generate a zone file. For example, mapping
  openid.kitenet.net to a CNAME to clam.kitenet.net, which is where
  the docker container for that service is located. Moving containers
  to a different host, or duplicating a container on multiple hosts
  would then update DNS too
* There is no way for a property of a docker container to require
  some property be met outside the container. For example, some servers
  need ntp installed for a good date source.
* Attributes can only be set in the top level property list for a Host.
  If an attribute is set inside a propertyList, it won't propigate out.
  Fix this. Probably the fix involves combining AttrProperty into Property.
  Then propertyList can gather the attributes from its list.