return a Result from Task functions

[jeremyandrews]

Tasks must be converted to return GooseTaskResult.

This allows the use of ? as it supports returning a GooseTaskError:

pub type GooseTaskResult = Result<(), GooseTaskError>;

Currently we define 3 errors:

/// Definition of all errors Goose Tasks can return.
#[derive(Debug)]
pub enum GooseTaskError {
    /// Contains any possible Reqwest library error.
    Reqwest(reqwest::Error),
    /// The request failed.
    RequestFailed,
    /// The request was canceled (this happens when the throttle is enabled and
    /// the load test finished).
    RequestCanceled,
}

[LionsAd]

Overall looks really great - think this is even ready to merge except for little things —

One thing:

I’d leave one example where we explictly call the debug_log — we optimized it away from all examples unless I miss something.

Maybe for a case before sending a request?

[jeremyandrews]

One thing:

I’d leave one example where we explictly call the debug_log — we optimized it away from all examples unless I miss something.

There was a commented out debug println!() in drupal_loadtest, which I converted to a commented out call to log_debug, along with a comment explaining why it's useful (if you're editing the load test).