node-show to show the instance_info field

The commit 7735ad404bb2849f5be738c2f8a536b1f817c6b7 for Ironic introduced
a new instance_info field to Nodes, this patch is adding the field to
be shown as part of the node-show command.

Change-Id: If719d955aec35f536dd19a231ccc2c5907a89b26
replace dict.iteritems() with six.iteritems(dict)

According to https://wiki.openstack.org/wiki/Python3 dict.iteritems()
should be replaced with six.iteritems(dict).

Change-Id: If7c7a286af559559060037aa80aea65b21c5c4ee
Merge "node-show to show the instance_info field"