Prepare for enabling H302 rule (api/object_storage)

We can use H302 rule but ignore it now. This commit prepares for
enabling H302 rule. But this commit modifies tempest/api/object_storage
only and excludes some violations[1] because if we fix all of them at
one time, it's hard to merge this commit.

[1]
 tempest.test.attr
 tempest.common.rest_client.RestClient
 tempest.common.rest_client.RestClientXML
 tempest.services.compute.xml.common.xml_to_json
 tempest.services.compute.xml.common.Element
 tempest.services.compute.xml.common.Document
 tempest.services.compute.xml.common.Text
 tempest.services.compute.xml.common.XMLNS_11
 tempest.services.compute.xml.common.XMLNS_V3
 tempest/clients.py

Change-Id: Ieaa403500e6d287ee2eac2ccdf921c7eca1e6e61
Merge "Prepare for enabling H302 rule (api/object_storage)"