Upstream RFE: https://bugs.launchpad.net/ironic/+bug/1554243

patch merged upstream; https://review.openstack.org/#/c/326620/

Update on the upstream status: code merged, present in Ocata (inspector version 5.0)
Changing status to ON_QA;

This was tested in a kvm virtual environment successfully. 

Steps:
install osp 12 undercloud with several nodes (i.e 3 controller, 2 compute, 1 <spare>)
On hypervisor, virsh detach-disk --domain <spare> --target vda --persistent
openstack baremetal import --json ~/instackenv.json  # contains 
openstack baremetal configure boot
openstack baremetal introspection bulk start
openstack baremetal list  # look for the uuid of <spare> used for 0 disk
openstack baremetal node show <uuid> | grep properties

As expected result:
The introspection succeeded now with one bare metal and property "u'local_gb': u'0'"

Additional testing to show that we can still detect and fail node with local_gb drive =0 by using device hints

This will set the device hints to seek out this case.

for i in `ironic node-list | awk '/None/ {print $2}'`;
do ironic node-update $i add properties/root_device='{"size": "> 1"}';done

follow with introspection

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHEA-2017:3462