All `net/rpc` requests go to `/minio`, so the existing
generic handler for reserved bucket check would essentially
erroneously send errors leading to distributed setups to
wait infinitely.
For `net/rpc` requests alone we should skip this check and
allow resource bucket names to be from `/minio` .
S3 only allows http headers with a size of 8 KB and user-defined metadata
with a size of 2 KB. This change adds a new API error and returns this
error to clients which sends to large http requests.
Fixes#4634
Make sure to skip reserved bucket names in `ListBuckets()`
current code didn't skip this properly and also generalize
this behavior for both XL and FS.
