Adding Authentication and Authorisation to the Admin API

Providing auth check by leveraging Zookeeper existing auth schemas and ACL check.

• Using HTTP authorization header to pass auth schema and auth info
• Supporting different auth schemas such as digest, x509, etc.
• Adding checkACLForAdminServerAPIs() to ZookeeperServer to perform auth check
• This feature will be used by the feature of On-Demand Zookeeper Backup and Restore with Streaming Capability

More info can be found https://mail.google.com/mail/u/0/#inbox/FMfcgzGqQSKPdTKzMxVHdCqprcsbRPDt