BluePrint: uniform assets management (revision of assets API)

[clebergnu]

This BluePrint will discuss a way to have a common API that will allow users to:

• Check if a resource is known
• Inquiry if a resource can be obtained
• Request the resource be obtained
• Check if a resource has been previously obtained (and is cached)

[wainersm]

Talking in private with @clebergnu , he mentions that vmimage and assets are planned to be merged. I have an idea to improve the usage of vmimage.get() that I will post here so it can (or not) be considered on the design of this blueprint.

TL;DR: users of vmimage.get() shouldn't be asked the checksum for a given distro.

Cleber proposed on [1] some changes to avocado_qemu tests so that users can choose the distro and version used on tests. You gonna see on those changes that a map is used to hold the checksum values. But it should not be an user concern; the vmimage has already the mapping of distro->image, and it can also hold the checksum information inside and hidden from users.

[1] https://mail.gnu.org/archive/html/qemu-devel/2021-04/msg02459.html