Agent HTTP Authentication

Now that the master has set a standard for http authentication, the agents should join the fun. Since a user must access the agent node to get to sandbox data, it and the rest of the endpoints should be configurable to require authentication, to prevent rogue users from viewing/modifying agent settings/data.
This will involve adding agent flags like `--authenticate_http --http_authenticators="basic"`
and even the equivalent of `--credentials` (maybe renamed)