entity.getAllAttributes() return everything

- Even if the AttributeSensor is unknown for a given key name, still
  return it.
- There’s a race where persister thread calls getAllAttributes() at
  same time as new attribute type is being added to entityType.
  Previously the sensor was not returned, so was not persisted.
RebindTestFixture: support for dumping mementoDir

- Create a mementoDirBackup field, in case wants to be used by
  sub-classes.
- Adds dumpMementoDir(File dir)
More logging for failing BindDnsServerIntegrationTest

- Fails non-deterministically on jenkins; can’t reproduce locally.
  Therefore adding logging to dump out a copy of the persistence dir,
  as it was at the point of rebind.
- Also terminates the old management context.