Rework tests

[Mia-Cross]

The deprecation of b_ssd volumes and unified snapshots had quite an impact on Instances default behaviors like, for example, the default type of the root volume has changed for offers that support both local and block storage.

This requires a few changes for Packer. The tests have been updated incrementally, so now all of them run checks on pretty much the same configuration. We should at least :

• remove redundant test cases
• add a test for local volumes
• add a test with both root_volume and block_volume defined
• rework TestComplete which is skipped since january 14th 2025 because of the snapshot_name argument that does not work anymore (probably because block volumes' and snapshots' names and sizes are not returned by the Instance API so that will require a bit of development outside the tests).
• implement new check functions for SBS volumes for the tests to be more reliable.