GetObject and GetObjectIPs are invoked by the Linksharing service to
display the shared object and its map. These two endpoint currently
require read permission.
There is a use case where an object can be shared with an access grant
that has only list permission. In such a case, the expectation is that
the linksharing service would still display the metadata of the shared
object (name, size, map), but the content would be still inaccessible.
See https://github.com/storj/gateway-mt/issues/209 for details.
This change allows GetObject and GetObjectIPs to require either read or
list permission to support the described use case.
Change-Id: I3477edc7bf8990e9848482890da047094c875d09
e709112eeb