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 <[email protected]>
Reviewed-by: Vikas Kedia <[email protected]>

spanner/row_test.go

@@ -31,7 +31,7 @@ import (
 )
 
 var (
-	tm    = time.Now().UTC()
+	tm    = time.Date(2016, 11, 15, 0, 0, 0, 0, time.UTC)
 	dt, _ = civil.ParseDate("2016-11-15")
 	// row contains a column for each unique Cloud Spanner type.
 	row = Row{