spanner: fix time.Time comparisons for upcoming Go1.9 monotonic times
spanner: fix time.Time comparisons for upcoming Go1.9 monotonic times

An upcoming change in Go1.9 changes the time.Time type to make a
measurement of both the wall clock and a monotonic clock. The
existence of a monotonic measurement makes it such that direct
equality and use of reflect.DeepEqual now fail. Fix by using a
specific date instead of time.Now, so that equality continues to
work. Do note that the documentation for time.Time has alwys
discouraged the use of == and instead recommended the use of the Equal
method.

See https://golang.org/design/12914-monotonic

Change-Id: I733678c5552e1618751b7c41d444230666def381
Reviewed-on: https://code-review.googlesource.com/11254
Reviewed-by: Damien Neil <7e091e9a80da888fcd7836fd3c6b7b85f4677c12@google.com>
Reviewed-by: Vikas Kedia <f6a34f50adc64ff8913356438469cce93f09537a@google.com>

googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go