Key Management service

Description: This worklog introduces a new keyring
             plugin -keyring_aws. The plugin will
             communicate with Amazon's AWS Key Management
             Service andfetch keys that can be used by
             MySQL server. It will provide ability to
             store/fetch/remove keys from Key Management
             service.

             In addition, Plugin also introduces two
             UDFs which provides ability to:
             - Rotate Customer Master Key
             - Reencrypt data keys using latest Customer
               Master Key.

Reviewed-By: Georgi Kodinov <georgi.kodinov@oracle.com>