XD-2026 Tweaks for storing admin metadata into zookeeper

https://jira.spring.io/browse/XD-2026

- New RuntimeRepository for admin metadata
- Following same concepts used in ContainerRepository
- Store real bind port from tomcat into this repository. RuntimeAttributes
  based on ContainerAttributes except group info has been removed.
- Metadata updates happen in DeploymentSupervisor where update logic
  is based on concepts from ContainerRegistrar.
- ZK path /xd/admins is moved over to /xd/adminelection and /xd/admins
  is now solely used for metadata in a same way that /xd/containers.
- ZooKeeperRuntimeRepository doesn't use caching because we don't
  expect a lot of runtime admin containers and we don't read that often.