Adding db.add_host() and workspace

- Adding add_host() Although Report host exists, this is a
straightforward method to metasploit-credential::creation::add_host()
- Add workspace.id to the responses of db.current_workspace and
db.workspace and  db.get_workspace
Removing add_host since it is not necessary :(

- Ups I did not needed this. I can get away with report_host and
report_client.
Return the workspace id in responses, lands #4142