message: [cli] Add input checking to verify waypoint provided
  Closes:
diff: @@ -64,13 +64,15 @@ struct Args {
  #[structopt(
  name = "waypoint",
  long,
  - help = "Explicitly specify the waypoint to use"
  + help = "Explicitly specify the waypoint to use",
  + required_unless = "waypoint_url"
  )]
  pub waypoint: Option<Waypoint>,
  #[structopt(
  name = "waypoint_url",
  long,
  - help = "URL for a file with the waypoint to use"
  + help = "URL for a file with the waypoint to use",
  + required_unless = "waypoint"
  )]
  pub waypoint_url: Option<String>,
  /// Verbose output.
  