Add barbican-manage command

This effort is to create a new barbican-manage command as a SINGLE admin command for all management functions in order to improve usability and extensibility in future. Other openstack services like Keystone and nova also provide similar commands for service admin to use.

Current following individual barbican commands will be consolidated and become sub-commands of new command "barbican-manage":
   - barbican-db-manage
   - pkcs11-key-generation
   - pkcs11-kek-rewrap
   - barbican-keystone-listener
   - barbican-retry
   - barbican-worker