Tightened IntegrationTest.WriteThenSync.
Tightened IntegrationTest.WriteThenSync.

jacobsa/ratelimit,mbrukman/gcsfuse,BanzaiMan/gcsfuse,GoogleCloudPlatform/gcsfuse,jacobsa/timeutil,kahing/gcsfuse,GoogleCloudPlatform/gcsfuse,BanzaiMan/gcsfuse,GoogleCloudPlatform/gcsfuse