XD-2038 Restore JDK6 compatibility

Avoid JDK7+ methods:
- Long.compare(x,y) in ZooKeeperContainerRepository
- Integer.compare(x,y) in ModuleDescriptor
- Collections.emptyIterator() in ChildPathIterator

Avoid this JDK7+ constant:
- PasswordUtils.UNICODE_CHARACTER_CLASS in PasswordUtils