swarm: handle device's expiration

If a device expires, a migration will regenerate the device's
certificate. In this case, the device certificate in swarms must
be updated.
So, the idea of this patch is to verify that the current certificate
in the repository for this device is still correct. If the device or
the member got invalidated, it tries to replace the current certificate
(updated via the migration). So that the new commits will still be valid.

Change-Id: I75b19b0edbb5601a758a73a4c4a44678d77295e1
GitLab: #684