Change for changing the global requirements https://review.openstack.org/#/c/146049/.

Adding nova for implementing HMAC-V4 support.
Nova expects a 'Signature' named header, which is now part of the 'Authorization'.

The issue can be reproduced with euca2ools:

# source /opt/stack/new/devstack/accrc/demo/demo
# euca-describe-keypairs --debug
2015-01-09 13:14:32,349 euca2ools [DEBUG]:Using access key provided by client.
2015-01-09 13:14:32,350 euca2ools [DEBUG]:Using secret key provided by client.
2015-01-09 13:14:32,351 euca2ools [DEBUG]:Method: POST
2015-01-09 13:14:32,351 euca2ools [DEBUG]:Path: /services/Cloud/
2015-01-09 13:14:32,352 euca2ools [DEBUG]:Data: 
2015-01-09 13:14:32,352 euca2ools [DEBUG]:Headers: {}
2015-01-09 13:14:32,352 euca2ools [DEBUG]:Host: 172.16.40.26
2015-01-09 13:14:32,353 euca2ools [DEBUG]:Port: 8773
2015-01-09 13:14:32,353 euca2ools [DEBUG]:Params: {'Action': 'DescribeKeyPairs', 'Version': '2010-08-31'}
2015-01-09 13:14:32,354 euca2ools [DEBUG]:establishing HTTP connection: kwargs={'port': 8773, 'timeout': 70}
2015-01-09 13:14:32,354 euca2ools [DEBUG]:Token: None
2015-01-09 13:14:32,355 euca2ools [DEBUG]:CanonicalRequest:
POST
/services/Cloud/

host:172.16.40.26:8773
x-amz-date:20150109T131432Z

host;x-amz-date
93691be75657638bb0188c9dd56303b89bb2818598871011d73eee11e14e0cec
2015-01-09 13:14:32,356 euca2ools [DEBUG]:StringToSign:
AWS4-HMAC-SHA256
20150109T131432Z
20150109/16/172/aws4_request
f8748433ff623a4e9cbd616ef63ebe6e506b36f1fd341a41983c955e59b82de7
2015-01-09 13:14:32,357 euca2ools [DEBUG]:Signature:
2dfa2098a8b893cec02f42b0e2abbe7ae5c6077ca1e5d8e1426cad5621e93e24
2015-01-09 13:14:32,357 euca2ools [DEBUG]:Final headers: {'Content-Length': '42', 'User-Agent': 'Boto/2.35.0 Python/2.7.5 Linux/3.17.7-200.fc20.x86_64', 'Host': '172.16.40.26:8773', 'X-Amz-Date': '20150109T131432Z', 'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8', 'Authorization': 'AWS4-HMAC-SHA256 Credential=6d8332aeeeb94e11bb23d4fc09c0a0f3/20150109/16/172/aws4_request,SignedHeaders=host;x-amz-date,Signature=2dfa2098a8b893cec02f42b0e2abbe7ae5c6077ca1e5d8e1426cad5621e93e24'}
send: 'POST /services/Cloud/ HTTP/1.1\r\nAccept-Encoding: identity\r\nContent-Length: 42\r\nUser-Agent: Boto/2.35.0 Python/2.7.5 Linux/3.17.7-200.fc20.x86_64\r\nHost: 172.16.40.26:8773\r\nX-Amz-Date: 20150109T131432Z\r\nContent-Type: application/x-www-form-urlencoded; charset=UTF-8\r\nAuthorization: AWS4-HMAC-SHA256 Credential=6d8332aeeeb94e11bb23d4fc09c0a0f3/20150109/16/172/aws4_request,SignedHeaders=host;x-amz-date,Signature=2dfa2098a8b893cec02f42b0e2abbe7ae5c6077ca1e5d8e1426cad5621e93e24\r\n\r\nAction=DescribeKeyPairs&Version=2010-08-31'
reply: 'HTTP/1.1 400 Bad Request\r\n'
header: Content-Type: text/xml
header: Content-Length: 203
header: Date: Fri, 09 Jan 2015 13:14:32 GMT
2015-01-09 13:14:32,365 euca2ools [DEBUG]:Response headers: [('date', 'Fri, 09 Jan 2015 13:14:32 GMT'), ('content-length', '203'), ('content-type', 'text/xml')]
2015-01-09 13:14:32,366 euca2ools [DEBUG]:<?xml version="1.0"?>
<Response><Errors><Error><Code>AuthFailure</Code><Message>Signature not provided</Message></Error></Errors><RequestID>req-5e70be08-7c34-4cf7-84f3-e907a7c4765c</RequestID></Response>
2015-01-09 13:14:32,366 euca2ools [ERROR]:400 Bad Request
2015-01-09 13:14:32,366 euca2ools [ERROR]:<?xml version="1.0"?>
<Response><Errors><Error><Code>AuthFailure</Code><Message>Signature not provided</Message></Error></Errors><RequestID>req-5e70be08-7c34-4cf7-84f3-e907a7c4765c</RequestID></Response>
AuthFailure: Signature not provided