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

Change-Id: I149f702d5b3ebae73b04deed4809939ab43c6adc
Merge "Don't raise HTTPForbidden on a multitenant environment"