This reverts changes in HADOOP-13230 to use S3Guard TTL in choosing when
to issue a HEAD request; fixing tests to compensate.
New org.apache.hadoop.fs.s3a.performance.OperationCost cost,
S3GUARD_NONAUTH_FILE_STATUS_PROBE for use in cost tests.
Contributed by Steve Loughran.
Change-Id: I418d55d2d2562a48b2a14ec7dee369db49b4e29e