releasetools: Add support for --override_timestamp. am: 9f884e6c55 am: 9ee7071553 am: d5de271e01 am: bd7cdf43e3 am: 912683668f am: c0413986fb
am: ae858a7899  -s ours

Change-Id: Idec8218fffcd638a8e8c9581b9d02197a2c30d92