---
fixes:
  - |
    Fixes `bug 2137673`_ where details about the fact that the user specified
    an incorrect configuration by requesting to attach to an external network are
    masked by "Failure prepping block device" since they do not have access to
    the whole backtrace.

    .. _bug 2137673: https://bugs.launchpad.net/nova/+bug/2137673
