text-html type is absent in TXT_ENC

If we get response with 404 status code and this response
contains in headers "content-type: text/html", NotFound
exception isn't raised.
Add 'text/html' type of content and convert value of
this parameter to lower case.

Change-Id: I632701f43219fa6c0efc6e95bf6007cb0a3ff0c2
Closes-Bug: #1269712
Remove X-Storage-Stoken from object_storage

We don't need it since X-Auth-Token is the one used and if defined as
None would crash.

Change-Id: I9487838996c861d99915132c4cb491fb66460593
Closes-Bug: 1266876
Merge "text-html type is absent in TXT_ENC"
Merge "Remove X-Storage-Stoken from object_storage"