Add upgrade testing

[jodh-intel]

Currently, packages are created using OBS for known good versions of the runtime and assets.

However, we need a way to generate packages for the runtime and assets for all release candidates to allow upgrade testing from version N to version N+1, to ensure it is possible to:

• Start (create) a Clear Containers from a previously-committed container.
• Create a new Clear Container with the new N+1 system.

Ideally, we'd have a public "testing" repository for .rpm and .deb files and once all tests (including upgrade tests pass successfully), those test packages would be promoted to the main repositories.

We expressly do not want users to install the testing packages - users should only install the official packages from the main repository.

This is related to #453.

[chavafg]

Now that we have releases every week, we should find a way of testing the OBS packages in an automated way. Will take a look this week.