Ceph Object Gateway can use keystone for authenticating user requests
to its S3-compatible API, but recent versions also provide two other
AWS-compatible APIs for managing user access: Security Token Service
(STS) and Identity and Access Management (IAM). These attempt to
authenticate requests with Keystone but always receive 403 Access
Denied because _calculate_signature_v4() in api/s3tokens.py only
accepts "s3" as the service name. This patch accepts any of "s3" or
"sts" or "iam" as valid service names.
Change-Id: I69f16ed55dd9852859307b701a8391ba1e71c042
Closes-Bug: #1897280