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.
If the admin encounters an exception with registration, it has no business being leader. Being the leader requires being connected to ZK.