Upgrades: Errors thrown by upgrade tasks should be reported to the end user, not ignored

As shown by CONF-20318, an upgrade task can throw an exception, but the upgrade will still complete "successfully".

In this case, the error made the instance unusable.

Instead of ignoring upgrade task errors, they should be reported to the end user. The text should report that problems were encountered during the upgrade, and the user should restore a back up and try again, and contact support if they get the same result.