Squashed commit of WebOb 1.5 and oslo.db fixes

Squashed commit of WebOb 1.5 and oslo.db fixes

Add testresources and testscenarios used by oslo.db fixture

If we use oslo.db fixtures, we'll need these 2 packages or
the next version of oslo.db release will break us.

Closes-Bug: #1503501
Change-Id: I8facdaf69c79b1b1ae4f9f64e9856e12f14440ed
(cherry picked from commit ec40c3b6ddbfa4912ca6e612558efaef6043f3ae)

Fix test_misc for WebOb 1.5

WebOb 1.5 was released at 2015-10-11. With this new version,
webob.exc.WSGIHTTPException() constructor now fails with a KeyError
when the HTTP status code is 0.

test_exceptions_raise() of test_misc tries to instanciate all
exceptions of cinder.exception. The problem is that
ConvertedException uses a default HTTP status code of 0.

Modify the default HTTP status code of ConvertedException to 400 to
fix the unit test. The bug is only in the test,
cinder/api/openstack/wsgi.py copies an existing HTTP code:

    Fault(exception.ConvertedException(code=ex_value.code,  ...)

Closes-Bug: #1505153
Change-Id: I1aec8038774828d48da4b0e831b390e33243809a
(cherry picked from commit 867fccf833ffc597aa986cb6ff1b3b5c1101b9ba)

Change default Exception code to 500

As a part of the fix for LP#1505153, the invalid
response of 0 was changed to 400 to fix a running
issue with the new version of WebOb.

It was pointed out after the fact  however that a
500 might be more appropriate here.

Additionally, other projects have implemented a 500
as the default so for the sake of consistency we should
consider doing the same.

This patch just changes the 400 to a 500 as the default
code.

Conflicts:
        cinder/tests/unit/test_exception.py

NOTE(mriedem): The conflict is due to 17802086f not being
in stable/liberty.

Change-Id: Ie486dc49c927f9b50f07c1fc562e89c090924a40
Closes-Bug: #1505488
(cherry picked from commit 9a7cbe540c94d54194194f4747a52b8211f6372e)