Remove force_tenant_isolation from FloatingIPAdminTestJSON

I don't see why force_tenant_isolation should be set to True
in FloatingIPAdminTestJSON, so this is to remove it.
Besides, if later we found the reason, we should add comments
for it.

Change-Id: Iac56eac444803ef06f115f9af1f66bbe8e831aa8
1 file changed