Port images metadata functionality to v3 API Part 1

This changeset only copies the v2 implementation file into the
appropriate v3 directory unchanged. The copy as-is will not be
loaded by either the v2 or v3 extension loaders. The second
changeset will then make the changes required for it to work as a
v3 extension.

This is being done in order to make reviewing of extension porting
easier as gerrit will display only what is actually changed for v3
rather than entirely new files

Note that this functionality will be moved from core to an
extension.  Consensus appears to be that we continue to need this
functionality for v3 because some deployers disable the public
image endpoint due security concerns and whether this will be
fixed in glance for Havana. Deployers can disable this extension
if they do not want it.

Partially implements blueprint nova-v3-api

Change-Id: I900ff0f93bb790f4f7bbac66bb2437906cb905f5
Merge "Port images metadata functionality to v3 API Part 1"