1. Adds two new fields to table ``nodes``.
2. Enable changes in conductor and api to execute
the methods for inspection.
3. Adds the default timeout `inspect_timeout` in
ironic.conf.sample file.
The new field 'last_inspected' has been renamed to
'inspection_finished_at' after discussion.
The ironic-client changes for 'inspect' to be
added to the list of node-set-provision-state valid
actions are being addressed by
https://review.openstack.org/#/c/148804
Implements : blueprint ironic-node-properties-discovery
DocImpact
Change-Id: If9aab90accf5a60ad3febbfc1f5d367eed987c13
6ecee36865