ringaccount: update account certificate through account migration

Multi-device account migration used a certificate without the CA flag
to sign the device certificate, preventing to properly validate the
device certificate chain.
Fix this by reusing the existing account migration API to ask for the
account password when the case is detected, placing the account in the
ERROR_NEED_MIGRATION state.
ERROR_NEED_MIGRATION could also be used for future account migrations,
when the password is needed to unlock the archive.

Bump OpenDHT to check the certificate expiration date.

Tuleap: #1434
Change-Id: I5527cf5bd31310d969819570cd984e622029fa71