Always use fixed notation for timestamps in pillowfight

Change-Id: I7384b59c44f87bbc8ccae88cc7eac042488365c5
Reviewed-on: http://review.couchbase.org/26781
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>