Container destroyed on snapcraft clean -s pull

[Sergio Schvezov]

Destroying the container on a `snapcraft clean` may be debatably ok but destroying it on a `snapcraft clean -s pull`, specially after being instructed to do so with:

```
The 'pull' step of 'osm-ro' is out of date:
The 'python-packages' part property appears to have changed.
In order to continue, please clean that part's 'pull' step by running:
snapcraft clean osm-ro -s pull
```

Is just a major slow down on productivity, more so when running on slow networks.

[Kyle Fazzari (kyrofa)]

This should be a matter of simply not assuming None == 'pull' for that parameter. Refactor suggestions in https://github.com/snapcore/snapcraft/pull/1587 will fix it.

[Sergio Schvezov (sergiusens)]

On lun, oct 30, 2017 at 11:25 AM, Kyle Fazzari <email address hidden>
wrote:
> This should be a matter of simply not assuming None == 'pull' for that
> parameter. Refactor suggestions in
> https://github.com/snapcore/snapcraft/pull/1587 will fix it.

This would be good to do. It is a real pain today to work in an
environment like this.

[Kyle Fazzari (kyrofa)]

Yeah... about that PR. Someone merged it ignoring my comment ;) .

[Cris Dywan (kalikiana)]

I'll propose another PR for this. Looking into another unit test for it before I do.

[Cris Dywan (kalikiana)]

https://github.com/snapcore/snapcraft/pull/1655