PR description

ObjectStorageObjectServiceImpl.put() and copy() read the ETag off the response but never checked its status, so an error -- a missing container (404), an ETag mismatch (422) and so on -- was silently returned as a null ETag instead of raising. Throw a ResponseException on a 4xx/5xx status so callers can detect and translate the failure.

Submitter checklist

Make sure that following is addressed to make the PR easier to process:

• If applicable, changes are covered by either a unit or a functional test.
• If applicable, changes ware verified manually against an OpenStack instance.
• If the change is API related, the PR description links to OpenStack API documentation of that particular endpoint/request (https://docs.openstack.org/api-quick-start/#current-api-versions).
• If the change concerns particular OpenStack service, its name is used as a PR name prefix (ex.: "Neutron: Add floatingIp port forwardings service").
• If the PR closes existing GitHub issue, PR name have prefix: Fix #NNN: .