When a bucket url like bucket.s3.amazonaws.com with bucket name bucket
is present in params passed into request_params method, it
should not dupplicate the subdomain.
current: bucket.bucket.s3.amazonaws.com
fix: bucket.s3.amazonaws.com
Fix test failure due to Hash#slice not present for ruby 2.3
Some S3 providers (e.g. Ceph) appear to send responses with lowercase
HTTP headers (e.g. content-length vs. Content-Length). This appears to
confuse fog-aws.
The attributes were not being loaded because the aliases did not contain
the lowercased version, and the attributes themselves use underscores
rather than dashes.
To fix this issue, we normalize the headers by fetching the value via
excon's case-insensitive lookup, storing the canonical key, and then
deleting other matches.
