Fix intermittent failures in sharder audit unit tests
Fix intermittent failures in sharder audit unit tests

Use predictable timestamp iterators to avoid some sharder audit tests
intermittently failing due to timestamps not advancing as assumed.

Change-Id: I1caea0925a6e9a853c7d6d7ad23c27bd37c5056f

openstack/swift,tipabu/swift,tipabu/swift,openstack/swift,openstack/swift,tipabu/swift,tipabu/swift,openstack/swift