Packaging: make sure to use the correct image for each distribution

What

Fix a problem with the packages matrix. We were wrongly compiling a ubuntu package on debian. This can cause a dependency error while installing this package.

Why

How

We use a the $DISTRIBUTION variable to select the correct base image.

Manually testing the MR

Check if each package is indeed compiled using the correct image.

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR