Make methods idempotent

[tiagodcc]

Description

As described in the actuator interface, all methods of the MachineAPI provider should be idempotent.

However, looking at the Create method of the provider, newly created server groups aren't deleted in case an error occurs later on. Additionally, the Delete method does not clean up empty server groups.

Additional Context

No response

Logs

Expected Behavior

• If the last server of a server group is deleted, the server group is deleted too.
• If a server groups is freshly created and the server provisioning fails, the server group is deleted.

Steps To Reproduce

No response

Versions

v0.3.0