Add support for downloading an exported instance snapshot

[sternik]

Hello team, this is a proposal to add a step to download an exported instance snapshot. In our process, we would like to upload the downloaded snapshot, e.g. to SOS, and then we will be able to use it to register the template on another account.

[yannprvst]

Hi @sternik !

Thank you for your proposal & contribution about our packer plugin.
For complete it, could you add the proper test file related to the snapshot download step (like https://github.com/exoscale/packer-plugin-exoscale/blob/main/builder/exoscale/step_export_snapshot_test.go for example) ?

Many thanks !

[exo-cedric]

Hi @sternik,

Thank you for this contribution! In addition to @yannprvst request, here are a few nitpicks which may be worth considering.

Cheers

[sternik]

Thank you for your proposal & contribution about our packer plugin. For complete it, could you add the proper test file related to the snapshot download step (like main/builder/exoscale/step_export_snapshot_test.go for example) ?

Hi @yannprvst , test added -> 54aad16 (#27)

[exo-cedric]

Thanks @sternik

I'm now working on integrating this in our acceptance tests and will get back to you.

[exo-cedric]

Updated acceptance tests pass (which I'll PR and merge separately).
Thanks again for this contribution!