Standardize obtaining boolean properties with defaults

We have several different ways to get boolean properties, using privileged calls.

"true".equalsIgnoreCase...GetPropertyAction("java.foo.bar","true");
BooleanAction()
and three different versions of getBooleanProperty in DistributionPointFetcher, ChannelImpl, Debug.

These were all developed over the years and in different unbundled variants, it would be good to standardize on one style.

This would be a good starter bug.