CBIDXT-94: updated unit-test case for timestamp.

snapshot fields are added to the Timestamp{} structure.

Change-Id: I0d1ad81c87787cb332d812c2c21fac80e0d2b290
Reviewed-on: http://review.couchbase.org/40490
Reviewed-by: John Liang <johliang00@gmail.com>
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Tested-by: Pratap Chakravarthy <prataprc@couchbase.com>