Don't raise HTTPForbidden on a multitenant environment

When getting public images in a multi-tenant environment, Swift raises
HTTPForbidden for chuncked images.

Based on swift documentation, rlistings directive turns listings on,
which is the desired behavior in this case.

Fixes bug 1170156

NOTE: Swift guys where consulted about this fix.

Change-Id: I149f702d5b3ebae73b04deed4809939ab43c6adc
Cherry-picked: 2d492e04be9e386e402ddde248d9a55c8d04a2bb
Merge "Don't raise HTTPForbidden on a multitenant environment" into stable/grizzly