Allow (and recommend) ENROLL state instead of maintenance mode for setting IPMI credentials

[Dmitry Tantsur]

This will require Ironic API 1.10, so we can't just deprecate using maintenance mode.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/219247

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/219247
Committed: https://git.openstack.org/cgit/openstack/ironic-inspector/commit/?id=676a5814117e346afc52ce9df1a329920074543a
Submitter: Jenkins
Branch: master

commit 676a5814117e346afc52ce9df1a329920074543a
Author: Dmitry Tantsur <email address hidden>
Date: Tue Sep 1 14:04:28 2015 +0200

    Revisit required provision states

    * Recommend using ENROLL for setting IPMI credentials
    * Deprecate using maintenance mode, will be dropped once we stop
      supporting Ironic Kilo
    * Drop bits related to Ironic Juno, we no longer support it
    * Clarify error message about wrong provision state, stop mentioning
      maintenance mode there

    Change-Id: I3a9d3ba24a32c7844cd6fd5e4f8ec4b15b2d9d20
    Closes-Bug: #1479331