A TokenKeyProvider for a Centralized Key Manager Server (BEE: bee-key-manager)

This is a key provider based on HADOOP-9331. HADOOP-9331 has designed a complete Hadoop crypto codec framework, but the key can only be retrieved from a local Java KeyStore file. To the convenience, we design a Centralized Key Manager Server (BEE: bee-key-manager) and user can use this TokenKeyProvider to retrieve keys from the Centralized Key Manager Server. By the way, to secure the key exchange, we leverage HTTPS + SPNego/SASL to protect the key exchange. To the detail design and usage, please refer to https://github.com/trendmicro/BEE.

Moreover, there are still much more requests about Hadoop Data Encryption (such as provide standalone module, support KMIP...etc.), if anyone has interested in those features, pleas let us know.