[RFE] Expose API node introspection state

it should be a issue, but we can get the introspection state via ironic API implicitly.

For example:
$ openstack baremetal node list
+--------------------------------------+--------+---------------+-------------+--------------------+-------------+
| UUID | Name | Instance UUID | Power State | Provisioning State | Maintenance |
+--------------------------------------+--------+---------------+-------------+--------------------+-------------+
| 399c52ce-e8cf-4202-a9c7-5bc4f95f2a24 | BM-132 | None | power on | inspecting | False |
+--------------------------------------+--------+---------------+-------------+--------------------+-------------+

$ openstack baremetal introspection status 399c52ce-e8cf-4202-a9c7-5bc4f95f2a24
+-------------+------------------------------------------------------------------------------------------------------------------+
| Field | Value |
+-------------+------------------------------------------------------------------------------------------------------------------+
| error | None |
| finished | False |
| finished_at | None |
| links | [{u'href': u'http://10.254.10.200:5050/v1/introspection/399c52ce-e8cf-4202-a9c7-5bc4f95f2a24', u'rel': u'self'}] |
| started_at | 2017-02-21T01:11:20 |
| uuid | 399c52ce-e8cf-4202-a9c7-5bc4f95f2a24 |
+-------------+------------------------------------------------------------------------------------------------------------------+

Seems it will require some changes in client, at least docs update

patch in ironic-inspector: https://review.openstack.org/#/c/436415/

Reviewed: https://review.openstack.org/436415
Committed: https://git.openstack.org/cgit/openstack/ironic-inspector/commit/?id=fc2e029fa6318384f840bdc8bc54894396308299
Submitter: Jenkins
Branch: master

commit fc2e029fa6318384f840bdc8bc54894396308299
Author: yaojun <email address hidden>
Date: Tue Feb 21 19:04:00 2017 +0800

    Adds node state to the API response data

    This adds the node state when the GET /v1/introspection/<node uuid or
    name> API is performed.

    Change-Id: I81c6834933f789cb644a854313aacaf49a4856a7
    Closes-Bug: #1665664

This issue was fixed in the openstack/ironic-inspector 6.0.0 release.