Only use dynamic delays for the crawler. Even though the max wait was 1 second the number
of waits could severely impact crawler speed.
Instead of relying on a global metric, we use the stateless local delays to keep the crawler
running at a speed more adjusted to current conditions.
The only case we keep it is before bitrot checks when enabled.
canonicalize the ENVs such that we can bring these ENVs
as part of the config values, as a subsequent change.
- fix location of per bucket usage to `.minio.sys/buckets/<bucket_name>/usage-cache.bin`
- fix location of the overall usage in `json` at `.minio.sys/buckets/.usage.json`
(avoid conflicts with a bucket named `usage.json` )
- fix location of the overall usage in `msgp` at `.minio.sys/buckets/.usage.bin`
(avoid conflicts with a bucket named `usage.bin`
