Implement 'enclaver run'

[russellhaering]

Screen.Recording.2022-10-31.at.2.37.14.PM.mov

I created #104 to reflect some future improvements I'd like to make.

[eyakubovich]

Some stylistic changes to think about.

[eyakubovich]

I'm still finding the best patterns myself but for these structs that have a state machine to them, but it might be better to consume self and then return a new object. For example:

impl RunWrapper {
    pub fn new() -> Result<Self> {
        ...
    }

    pub async fn run_enclave_image(self, ...) -> Result<RunHandle> {
         ...
    }
}

struct RunHandle {
}

impl RunHandle {
    pub async cleanup(self) {
       ...
    }
}

This should remove the Option fields in your structs since they model "not for this state".

Alternatively you can take in a CancellationToken so you end up with:

impl RunWrapper {
    pub fn new() -> Result<Self> {
        ...
    }

    pub async fn run_enclave_image(self, token: CancellationToken) -> Result<()> {
         ...
    }
}

and no cleanup to forget. However you have to make sure you .await to completion.

[eyakubovich]

If shutdown_signal comes,the run_enclaver_image will get aborted at some inner .await. However you don't know which one so cleanup now has to account for every case.