Merge ~kissiel/checkbox/+git/checkbox-configure:qol-changes into ~checkbox-dev/checkbox/+git/checkbox-configure:master

I fixed a problem with generating classic snap with embedded provider.
Squashed and pushed.

I added a few comments inline.

In addition, I played a little with this tool (one of the project I have requires the creation of checkbox snaps). When I run:

    ./configure project=test base=core20

it does a bunch of things, and then:

-----------------------------------
$ tree checkbox-test
checkbox-test
├── config
│   └── config_vars
├── launchers
│   ├── checkbox-cli-wrapper
│   ├── configure
│   ├── shell-wrapper
│   ├── test-runner
│   ├── test-runner-automated
│   └── wrapper_local
├── README.md
└── snap
    ├── hooks
    │   ├── configure
    │   └── install
    ├── plugins
    │   └── checkbox_provider.py
    ├── snapcraft_classic.yaml.in_v2
    └── snapcraft.yaml

5 directories, 13 files
-----------------------------------

→ is the `snapcraft_classic.yaml.in_v2` file expected here? How about `README.md`?

-----------------------------------
$ tree checkbox-test-classic/
checkbox-test-classic/
├── checkbox-provider-template
│   └── units
│   └── device
│   └── jobs.pxu
├── config
│   └── config_vars
├── launchers
│   ├── checkbox-cli-wrapper
│   ├── checkbox-slave
│   ├── configure
│   ├── hook-wrapper
│   ├── shell-wrapper
│   ├── test-runner
│   ├── test-runner-automated
│   └── wrapper_local
├── launchers_v2
│   ├── checkbox-cli-wrapper
│   ├── configure.in_classic
│   ├── shell-wrapper
│   ├── test-runner-automated.in
│   ├── test-runner-automated.in_classic
│   ├── test-runner.in
│   ├── test-runner.in_classic
│   ├── wrapper_local.in
│   └── wrapper_local.in_classic
├── README.md
└── snap
    ├── hooks
    │   ├── configure
    │   ├── install
    │   └── remove
    ├── plugins
    │   └── checkbox_provider.py
    ├── snapcraft.yaml
    └── snapcraft.yaml.in_v2

9 directories, 26 files
-----------------------------------

→ Looks like a lot of files have been copied over, but I'm not sure if that's normal:

- launchers_v2/*
- README.md
- snap/snapcraft.yaml.in_v2

I've fixed the problems listed by Pierre. Squashed and pushed.

Thanks for fixing these! It works better now :)

I noticed (only now, sorry!) that the markdown syntax was a bit off. Copypasting the README file in StackEdit for instance does not lead to a good HTML markup. I added some inline comments, but this happens eslewhere in the doc. Basically, syntax like

``` blablabla ```

should become

```
blablabla
```

otherwise it's not converted to a code block, but in an inline element in HTML.

Also, there is a reference to an internal project, I guess that should be removed (it's not useful for the understanding of the line anyway).